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Commit 11d21456 authored by Markus Stockhausen's avatar Markus Stockhausen Committed by Alistair Strachan
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UPSTREAM: readahead: stricter check for bdi io_pages 



ondemand_readahead() checks bdi->io_pages to cap the maximum pages
that need to be processed. This works until the readit section. If
we would do an async only readahead (async size = sync size) and
target is at beginning of window we expand the pages by another
get_next_ra_size() pages. Btrace for large reads shows that kernel
always issues a doubled size read at the beginning of processing.
Add an additional check for io_pages in the lower part of the func.
The fix helps devices that hard limit bio pages and rely on proper
handling of max_hw_read_sectors (e.g. older FusionIO cards). For
that reason it could qualify for stable.

Fixes: 9491ae4a ("mm: don't cap request size based on read-ahead setting")
Change-Id: If111344b54897555085c2a6c442d697069962f11
Cc: stable@vger.kernel.org
Signed-off-by: default avatarMarkus Stockhausen <stockhausen@collogia.de>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
Signed-off-by: default avatarJaegeuk Kim <jaegeuk@google.com>
parent 1e6563ff

mm/readahead.c

+10 −2
Original line number Original line Diff line number Diff line
@@ -380,6 +380,7 @@ ondemand_readahead(struct address_space *mapping, 
{

{

	struct backing_dev_info *bdi = inode_to_bdi(mapping->host);

	struct backing_dev_info *bdi = inode_to_bdi(mapping->host);

	unsigned long max_pages = ra->ra_pages;

	unsigned long max_pages = ra->ra_pages;

	unsigned long add_pages;

	pgoff_t prev_offset;

	pgoff_t prev_offset;





	/*

	/*
@@ -469,10 +470,17 @@ ondemand_readahead(struct address_space *mapping, 
	 * Will this read hit the readahead marker made by itself?

	 * Will this read hit the readahead marker made by itself?

	 * If so, trigger the readahead marker hit now, and merge

	 * If so, trigger the readahead marker hit now, and merge

	 * the resulted next readahead window into the current one.

	 * the resulted next readahead window into the current one.

	 * Take care of maximum IO pages as above.

	 */

	 */

	if (offset == ra->start && ra->size == ra->async_size) {

	if (offset == ra->start && ra->size == ra->async_size) {

		ra->async_size = get_next_ra_size(ra, max_pages);

		add_pages = get_next_ra_size(ra, max_pages);

		ra->size += ra->async_size;

		if (ra->size + add_pages <= max_pages) {

			ra->async_size = add_pages;

			ra->size += add_pages;

		} else {

			ra->size = max_pages;

			ra->async_size = max_pages >> 1;

		}

	}

	}





	return ra_submit(ra, mapping, filp);

	return ra_submit(ra, mapping, filp);