mm/filemap.c: generic_file_buffered_read() now uses find_get_pages_contig
Convert generic_file_buffered_read() to get pages to read from in batches, and then copy data to userspace from many pages at once - in particular, we now don't touch any cachelines that might be contended while we're in the loop to copy data to userspace. This is is a performance improvement on workloads that do buffered reads with large blocksizes, and a very large performance improvement if that file is also being accessed concurrently by different threads. On smaller reads (512 bytes), there's a very small performance improvement (1%, within the margin of error). akpm: kernel test robot found a 32% speedup on one test: https://lkml.kernel.org/r/20201030081456.GY31092@shao2-debian Link: https://lkml.kernel.org/r/20201025212949.602194-3-kent.overstreet@gmail.com Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: kernel test robot <rong.a.chen@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Kent Overstreet
Linus Torvalds
parent
723ef24b9b
commit
06c0444290
317
mm/filemap.c
317
mm/filemap.c
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@ -2176,67 +2176,6 @@ static int lock_page_for_iocb(struct kiocb *iocb, struct page *page)
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return lock_page_killable(page);
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}
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static int generic_file_buffered_read_page_ok(struct kiocb *iocb,
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struct iov_iter *iter,
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struct page *page)
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{
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struct address_space *mapping = iocb->ki_filp->f_mapping;
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struct inode *inode = mapping->host;
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struct file_ra_state *ra = &iocb->ki_filp->f_ra;
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unsigned int offset = iocb->ki_pos & ~PAGE_MASK;
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unsigned int bytes, copied;
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loff_t isize, end_offset;
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BUG_ON(iocb->ki_pos >> PAGE_SHIFT != page->index);
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/*
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* i_size must be checked after we know the page is Uptodate.
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*
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* Checking i_size after the check allows us to calculate
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* the correct value for "bytes", which means the zero-filled
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* part of the page is not copied back to userspace (unless
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* another truncate extends the file - this is desired though).
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*/
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isize = i_size_read(inode);
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if (unlikely(iocb->ki_pos >= isize))
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return 1;
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end_offset = min_t(loff_t, isize, iocb->ki_pos + iter->count);
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bytes = min_t(loff_t, end_offset - iocb->ki_pos, PAGE_SIZE - offset);
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/* If users can be writing to this page using arbitrary
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* virtual addresses, take care about potential aliasing
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* before reading the page on the kernel side.
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*/
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if (mapping_writably_mapped(mapping))
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flush_dcache_page(page);
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/*
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* Ok, we have the page, and it's up-to-date, so
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* now we can copy it to user space...
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*/
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copied = copy_page_to_iter(page, offset, bytes, iter);
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iocb->ki_pos += copied;
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/*
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* When a sequential read accesses a page several times,
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* only mark it as accessed the first time.
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*/
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if (iocb->ki_pos >> PAGE_SHIFT != ra->prev_pos >> PAGE_SHIFT)
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mark_page_accessed(page);
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ra->prev_pos = iocb->ki_pos;
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if (copied < bytes)
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return -EFAULT;
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return !iov_iter_count(iter) || iocb->ki_pos == isize;
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}
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static struct page *
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generic_file_buffered_read_readpage(struct kiocb *iocb,
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struct file *filp,
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@ -2394,6 +2333,92 @@ generic_file_buffered_read_no_cached_page(struct kiocb *iocb,
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return generic_file_buffered_read_readpage(iocb, filp, mapping, page);
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}
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static int generic_file_buffered_read_get_pages(struct kiocb *iocb,
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struct iov_iter *iter,
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struct page **pages,
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unsigned int nr)
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{
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struct file *filp = iocb->ki_filp;
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struct address_space *mapping = filp->f_mapping;
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struct file_ra_state *ra = &filp->f_ra;
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pgoff_t index = iocb->ki_pos >> PAGE_SHIFT;
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pgoff_t last_index = (iocb->ki_pos + iter->count + PAGE_SIZE-1) >> PAGE_SHIFT;
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int i, j, nr_got, err = 0;
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nr = min_t(unsigned long, last_index - index, nr);
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find_page:
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if (fatal_signal_pending(current))
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return -EINTR;
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nr_got = find_get_pages_contig(mapping, index, nr, pages);
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if (nr_got)
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goto got_pages;
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if (iocb->ki_flags & IOCB_NOIO)
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return -EAGAIN;
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page_cache_sync_readahead(mapping, ra, filp, index, last_index - index);
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nr_got = find_get_pages_contig(mapping, index, nr, pages);
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if (nr_got)
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goto got_pages;
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pages[0] = generic_file_buffered_read_no_cached_page(iocb, iter);
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err = PTR_ERR_OR_ZERO(pages[0]);
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if (!IS_ERR_OR_NULL(pages[0]))
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nr_got = 1;
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got_pages:
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for (i = 0; i < nr_got; i++) {
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struct page *page = pages[i];
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pgoff_t pg_index = index + i;
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loff_t pg_pos = max(iocb->ki_pos,
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(loff_t) pg_index << PAGE_SHIFT);
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loff_t pg_count = iocb->ki_pos + iter->count - pg_pos;
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if (PageReadahead(page)) {
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if (iocb->ki_flags & IOCB_NOIO) {
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for (j = i; j < nr_got; j++)
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put_page(pages[j]);
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nr_got = i;
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err = -EAGAIN;
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break;
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}
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page_cache_async_readahead(mapping, ra, filp, page,
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pg_index, last_index - pg_index);
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}
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if (!PageUptodate(page)) {
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if ((iocb->ki_flags & IOCB_NOWAIT) ||
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((iocb->ki_flags & IOCB_WAITQ) && i)) {
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for (j = i; j < nr_got; j++)
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put_page(pages[j]);
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nr_got = i;
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err = -EAGAIN;
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break;
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}
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page = generic_file_buffered_read_pagenotuptodate(iocb,
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filp, iter, page, pg_pos, pg_count);
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if (IS_ERR_OR_NULL(page)) {
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for (j = i + 1; j < nr_got; j++)
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put_page(pages[j]);
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nr_got = i;
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err = PTR_ERR_OR_ZERO(page);
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break;
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}
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}
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}
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if (likely(nr_got))
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return nr_got;
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if (err)
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return err;
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/*
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* No pages and no error means we raced and should retry:
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*/
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goto find_page;
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}
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/**
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* generic_file_buffered_read - generic file read routine
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* @iocb: the iocb to read
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@ -2414,104 +2439,116 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
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struct iov_iter *iter, ssize_t written)
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{
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struct file *filp = iocb->ki_filp;
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struct file_ra_state *ra = &filp->f_ra;
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struct address_space *mapping = filp->f_mapping;
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struct inode *inode = mapping->host;
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struct file_ra_state *ra = &filp->f_ra;
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size_t orig_count = iov_iter_count(iter);
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pgoff_t last_index;
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int error = 0;
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struct page *pages_onstack[PAGEVEC_SIZE], **pages = NULL;
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unsigned int nr_pages = min_t(unsigned int, 512,
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((iocb->ki_pos + iter->count + PAGE_SIZE - 1) >> PAGE_SHIFT) -
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(iocb->ki_pos >> PAGE_SHIFT));
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int i, pg_nr, error = 0;
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bool writably_mapped;
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loff_t isize, end_offset;
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if (unlikely(iocb->ki_pos >= inode->i_sb->s_maxbytes))
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return 0;
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iov_iter_truncate(iter, inode->i_sb->s_maxbytes);
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last_index = (iocb->ki_pos + iter->count + PAGE_SIZE-1) >> PAGE_SHIFT;
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if (nr_pages > ARRAY_SIZE(pages_onstack))
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pages = kmalloc_array(nr_pages, sizeof(void *), GFP_KERNEL);
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/*
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* If we've already successfully copied some data, then we
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* can no longer safely return -EIOCBQUEUED. Hence mark
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* an async read NOWAIT at that point.
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*/
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if (written && (iocb->ki_flags & IOCB_WAITQ))
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iocb->ki_flags |= IOCB_NOWAIT;
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for (;;) {
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pgoff_t index = iocb->ki_pos >> PAGE_SHIFT;
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struct page *page;
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if (!pages) {
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pages = pages_onstack;
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nr_pages = min_t(unsigned int, nr_pages, ARRAY_SIZE(pages_onstack));
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}
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do {
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cond_resched();
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find_page:
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if (fatal_signal_pending(current)) {
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error = -EINTR;
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goto out;
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/*
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* If we've already successfully copied some data, then we
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* can no longer safely return -EIOCBQUEUED. Hence mark
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* an async read NOWAIT at that point.
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*/
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if ((iocb->ki_flags & IOCB_WAITQ) && written)
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iocb->ki_flags |= IOCB_NOWAIT;
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i = 0;
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pg_nr = generic_file_buffered_read_get_pages(iocb, iter,
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pages, nr_pages);
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if (pg_nr < 0) {
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error = pg_nr;
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break;
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}
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/*
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* We can't return -EIOCBQUEUED once we've done some work, so
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* ensure we don't block:
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* i_size must be checked after we know the pages are Uptodate.
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*
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* Checking i_size after the check allows us to calculate
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* the correct value for "nr", which means the zero-filled
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* part of the page is not copied back to userspace (unless
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* another truncate extends the file - this is desired though).
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*/
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if ((iocb->ki_flags & IOCB_WAITQ) &&
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(written + orig_count - iov_iter_count(iter)))
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iocb->ki_flags |= IOCB_NOWAIT;
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isize = i_size_read(inode);
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if (unlikely(iocb->ki_pos >= isize))
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goto put_pages;
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page = find_get_page(mapping, index);
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if (!page) {
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if (iocb->ki_flags & IOCB_NOIO)
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goto would_block;
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page_cache_sync_readahead(mapping,
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ra, filp,
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index, last_index - index);
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page = find_get_page(mapping, index);
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if (unlikely(page == NULL)) {
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page = generic_file_buffered_read_no_cached_page(iocb, iter);
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if (!page)
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goto find_page;
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if (IS_ERR(page)) {
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error = PTR_ERR(page);
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goto out;
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}
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}
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}
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if (PageReadahead(page)) {
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if (iocb->ki_flags & IOCB_NOIO) {
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put_page(page);
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goto out;
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}
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page_cache_async_readahead(mapping,
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ra, filp, page,
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index, last_index - index);
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}
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if (!PageUptodate(page)) {
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if (iocb->ki_flags & IOCB_NOWAIT) {
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put_page(page);
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error = -EAGAIN;
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goto out;
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}
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page = generic_file_buffered_read_pagenotuptodate(iocb,
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filp, iter, page, iocb->ki_pos, iter->count);
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if (!page)
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goto find_page;
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if (IS_ERR(page)) {
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error = PTR_ERR(page);
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goto out;
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end_offset = min_t(loff_t, isize, iocb->ki_pos + iter->count);
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while ((iocb->ki_pos >> PAGE_SHIFT) + pg_nr >
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(end_offset + PAGE_SIZE - 1) >> PAGE_SHIFT)
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put_page(pages[--pg_nr]);
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/*
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* Once we start copying data, we don't want to be touching any
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* cachelines that might be contended:
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*/
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writably_mapped = mapping_writably_mapped(mapping);
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/*
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* When a sequential read accesses a page several times, only
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* mark it as accessed the first time.
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*/
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if (iocb->ki_pos >> PAGE_SHIFT !=
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ra->prev_pos >> PAGE_SHIFT)
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mark_page_accessed(pages[0]);
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for (i = 1; i < pg_nr; i++)
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mark_page_accessed(pages[i]);
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for (i = 0; i < pg_nr; i++) {
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unsigned int offset = iocb->ki_pos & ~PAGE_MASK;
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unsigned int bytes = min_t(loff_t, end_offset - iocb->ki_pos,
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PAGE_SIZE - offset);
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unsigned int copied;
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/*
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* If users can be writing to this page using arbitrary
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* virtual addresses, take care about potential aliasing
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* before reading the page on the kernel side.
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*/
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if (writably_mapped)
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flush_dcache_page(pages[i]);
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copied = copy_page_to_iter(pages[i], offset, bytes, iter);
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written += copied;
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iocb->ki_pos += copied;
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ra->prev_pos = iocb->ki_pos;
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if (copied < bytes) {
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error = -EFAULT;
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break;
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}
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}
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put_pages:
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for (i = 0; i < pg_nr; i++)
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put_page(pages[i]);
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} while (iov_iter_count(iter) && iocb->ki_pos < isize && !error);
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error = generic_file_buffered_read_page_ok(iocb, iter, page);
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put_page(page);
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if (error) {
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if (error > 0)
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error = 0;
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goto out;
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}
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}
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would_block:
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error = -EAGAIN;
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out:
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file_accessed(filp);
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written += orig_count - iov_iter_count(iter);
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if (pages != pages_onstack)
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kfree(pages);
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return written ? written : error;
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}
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