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mm/filemap: add mapping_seek_hole_data 

Rewrite shmem_seek_hole_data() and move it to filemap.c.

[willy@infradead.org: don't put an xa_is_value() page]
  Link: https://lkml.kernel.org/r/20201124041507.28996-4-willy@infradead.org

Link: https://lkml.kernel.org/r/20201112212641.27837-8-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Matthew Wilcox (Oracle) 2021-02-25 17:15:48 -08:00 committed by Linus Torvalds
parent c7bad633e6
commit 41139aa4c3
3 changed files with 82 additions and 70 deletions
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2
include/linux/pagemap.h
View File

@ -760,6 +760,8 @@ extern void __delete_from_page_cache(struct page *page, void *shadow);
void replace_page_cache_page(struct page *old, struct page *new);
void delete_from_page_cache_batch(struct address_space *mapping,
struct pagevec *pvec);
loff_t mapping_seek_hole_data(struct address_space *, loff_t start, loff_t end,
int whence);
/*
* Like add_to_page_cache_locked, but used to add newly allocated pages:

76
mm/filemap.c
View File

@ -2553,6 +2553,82 @@ generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
}
EXPORT_SYMBOL(generic_file_read_iter);
static inline bool page_seek_match(struct page *page, bool seek_data)
{
if (xa_is_value(page) || PageUptodate(page))
return seek_data;
return !seek_data;
}
static inline
unsigned int seek_page_size(struct xa_state *xas, struct page *page)
{
if (xa_is_value(page))
return PAGE_SIZE << xa_get_order(xas->xa, xas->xa_index);
return thp_size(page);
}
/**
* mapping_seek_hole_data - Seek for SEEK_DATA / SEEK_HOLE in the page cache.
* @mapping: Address space to search.
* @start: First byte to consider.
* @end: Limit of search (exclusive).
* @whence: Either SEEK_HOLE or SEEK_DATA.
*
* If the page cache knows which blocks contain holes and which blocks
* contain data, your filesystem can use this function to implement
* SEEK_HOLE and SEEK_DATA. This is useful for filesystems which are
* entirely memory-based such as tmpfs, and filesystems which support
* unwritten extents.
*
* Return: The requested offset on successs, or -ENXIO if @whence specifies
* SEEK_DATA and there is no data after @start. There is an implicit hole
* after @end - 1, so SEEK_HOLE returns @end if all the bytes between @start
* and @end contain data.
*/
loff_t mapping_seek_hole_data(struct address_space *mapping, loff_t start,
loff_t end, int whence)
{
XA_STATE(xas, &mapping->i_pages, start >> PAGE_SHIFT);
pgoff_t max = (end - 1) / PAGE_SIZE;
bool seek_data = (whence == SEEK_DATA);
struct page *page;
if (end <= start)
return -ENXIO;
rcu_read_lock();
while ((page = find_get_entry(&xas, max, XA_PRESENT))) {
loff_t pos = xas.xa_index * PAGE_SIZE;
if (start < pos) {
if (!seek_data)
goto unlock;
start = pos;
}
if (page_seek_match(page, seek_data))
goto unlock;
start = pos + seek_page_size(&xas, page);
if (!xa_is_value(page))
put_page(page);
}
rcu_read_unlock();
if (seek_data)
return -ENXIO;
goto out;
unlock:
rcu_read_unlock();
if (!xa_is_value(page))
put_page(page);
out:
if (start > end)
return end;
return start;
}
#ifdef CONFIG_MMU
#define MMAP_LOTSAMISS (100)
/*

74
mm/shmem.c
View File

@ -2668,86 +2668,20 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
return retval ? retval : error;
}
/*
* llseek SEEK_DATA or SEEK_HOLE through the page cache.
*/
static pgoff_t shmem_seek_hole_data(struct address_space *mapping,
pgoff_t index, pgoff_t end, int whence)
{
struct page *page;
struct pagevec pvec;
pgoff_t indices[PAGEVEC_SIZE];
bool done = false;
int i;
pagevec_init(&pvec);
pvec.nr = 1; /* start small: we may be there already */
while (!done) {
pvec.nr = find_get_entries(mapping, index,
pvec.nr, pvec.pages, indices);
if (!pvec.nr) {
if (whence == SEEK_DATA)
index = end;
break;
}
for (i = 0; i < pvec.nr; i++, index++) {
if (index < indices[i]) {
if (whence == SEEK_HOLE) {
done = true;
break;
}
index = indices[i];
}
page = pvec.pages[i];
if (page && !xa_is_value(page)) {
if (!PageUptodate(page))
page = NULL;
}
if (index >= end ||
(page && whence == SEEK_DATA) ||
(!page && whence == SEEK_HOLE)) {
done = true;
break;
}
}
pagevec_remove_exceptionals(&pvec);
pagevec_release(&pvec);
pvec.nr = PAGEVEC_SIZE;
cond_resched();
}
return index;
}
static loff_t shmem_file_llseek(struct file *file, loff_t offset, int whence)
{
struct address_space *mapping = file->f_mapping;
struct inode *inode = mapping->host;
pgoff_t start, end;
loff_t new_offset;
if (whence != SEEK_DATA && whence != SEEK_HOLE)
return generic_file_llseek_size(file, offset, whence,
MAX_LFS_FILESIZE, i_size_read(inode));
if (offset < 0)
return -ENXIO;
inode_lock(inode);
/* We're holding i_mutex so we can access i_size directly */
if (offset < 0 || offset >= inode->i_size)
offset = -ENXIO;
else {
start = offset >> PAGE_SHIFT;
end = (inode->i_size + PAGE_SIZE - 1) >> PAGE_SHIFT;
new_offset = shmem_seek_hole_data(mapping, start, end, whence);
new_offset <<= PAGE_SHIFT;
if (new_offset > offset) {
if (new_offset < inode->i_size)
offset = new_offset;
else if (whence == SEEK_DATA)
offset = -ENXIO;
else
offset = inode->i_size;
}
}
offset = mapping_seek_hole_data(mapping, offset, inode->i_size, whence);
if (offset >= 0)
offset = vfs_setpos(file, offset, MAX_LFS_FILESIZE);
inode_unlock(inode);