lkml.org 
[lkml]   [2018]   [Sep]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 4.18 012/145] readahead: stricter check for bdi io_pages
Date
4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Markus Stockhausen <stockhausen@collogia.de>

commit dc30b96ab6d569060741572cf30517d3179429a8 upstream.

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")
Cc: stable@vger.kernel.org
Signed-off-by: Markus Stockhausen stockhausen@collogia.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
mm/readahead.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -385,6 +385,7 @@ ondemand_readahead(struct address_space
{
struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
unsigned long max_pages = ra->ra_pages;
+ unsigned long add_pages;
pgoff_t prev_offset;

/*
@@ -474,10 +475,17 @@ readit:
* Will this read hit the readahead marker made by itself?
* If so, trigger the readahead marker hit now, and merge
* 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) {
- ra->async_size = get_next_ra_size(ra, max_pages);
- ra->size += ra->async_size;
+ add_pages = get_next_ra_size(ra, max_pages);
+ 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);

\
 
 \ /
  Last update: 2018-09-08 10:03    [W:0.453 / U:0.928 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site