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mm: split ->readpages calls to avoid non-contiguous pages lists 

That way file systems don't have to go spotting for non-contiguous pages
and work around them.  It also kicks off I/O earlier, allowing it to
finish earlier and reduce latency.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
This commit is contained in:
Christoph Hellwig 2018-06-01 09:03:06 -07:00 committed by Darrick J. Wong
parent c534aa3fdd
commit b3751e6ab4
1 changed files with 13 additions and 3 deletions
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16
mm/readahead.c
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@ -140,8 +140,8 @@ static int read_pages(struct address_space *mapping, struct file *filp,
}
/*
* __do_page_cache_readahead() actually reads a chunk of disk. It allocates all
* the pages first, then submits them all for I/O. This avoids the very bad
* __do_page_cache_readahead() actually reads a chunk of disk. It allocates
* the pages first, then submits them for I/O. This avoids the very bad
* behaviour which would occur if page allocations are causing VM writeback.
* We really don't want to intermingle reads and writes like that.
*
@ -177,8 +177,18 @@ unsigned int __do_page_cache_readahead(struct address_space *mapping,
rcu_read_lock();
page = radix_tree_lookup(&mapping->i_pages, page_offset);
rcu_read_unlock();
if (page && !radix_tree_exceptional_entry(page))
if (page && !radix_tree_exceptional_entry(page)) {
/*
* Page already present? Kick off the current batch of
* contiguous pages before continuing with the next
* batch.
*/
if (nr_pages)
read_pages(mapping, filp, &page_pool, nr_pages,
gfp_mask);
nr_pages = 0;
continue;
}
page = __page_cache_alloc(gfp_mask);
if (!page)