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authorJens Axboe <axboe@fb.com>2016-12-13 03:43:26 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2016-12-13 05:55:08 +0300
commit9491ae4aade6814afcfa67f4eb3e3342c2b39750 (patch)
treece3bd5d3a5c504548583ce581525011594589d59 /include/linux/backing-dev-defs.h
parentf1f5929cd9715c1cdfe07a890f12ac7d2c5304ec (diff)
downloadlinux-9491ae4aade6814afcfa67f4eb3e3342c2b39750.tar.xz
mm: don't cap request size based on read-ahead setting
We ran into a funky issue, where someone doing 256K buffered reads saw 128K requests at the device level. Turns out it is read-ahead capping the request size, since we use 128K as the default setting. This doesn't make a lot of sense - if someone is issuing 256K reads, they should see 256K reads, regardless of the read-ahead setting, if the underlying device can support a 256K read in a single command. This patch introduces a bdi hint, io_pages. This is the soft max IO size for the lower level, I've hooked it up to the bdev settings here. Read-ahead is modified to issue the maximum of the user request size, and the read-ahead max size, but capped to the max request size on the device side. The latter is done to avoid reading ahead too much, if the application asks for a huge read. With this patch, the kernel behaves like the application expects. Link: http://lkml.kernel.org/r/1479498073-8657-1-git-send-email-axboe@fb.com Signed-off-by: Jens Axboe <axboe@fb.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/backing-dev-defs.h')
-rw-r--r--include/linux/backing-dev-defs.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
index c357f27d5483..b8144b2d59ce 100644
--- a/include/linux/backing-dev-defs.h
+++ b/include/linux/backing-dev-defs.h
@@ -136,6 +136,7 @@ struct bdi_writeback {
struct backing_dev_info {
struct list_head bdi_list;
unsigned long ra_pages; /* max readahead in PAGE_SIZE units */
+ unsigned long io_pages; /* max allowed IO size */
unsigned int capabilities; /* Device capabilities */
congested_fn *congested_fn; /* Function pointer if device is md/dm */
void *congested_data; /* Pointer to aux data for congested func */