From: Tejun Heo <tj@kernel.org>
To: axboe@kernel.dk
Cc: linux-kernel@vger.kernel.org, jack@suse.cz, hch@infradead.org,
hannes@cmpxchg.org, linux-fsdevel@vger.kernel.org,
vgoyal@redhat.com, lizefan@huawei.com, cgroups@vger.kernel.org,
linux-mm@kvack.org, mhocko@suse.cz, clm@fb.com,
fengguang.wu@intel.com, david@fromorbit.com, gthelen@google.com,
Tejun Heo <tj@kernel.org>,
Vladimir Davydov <vdavydov@parallels.com>
Subject: [PATCH 18/18] mm: vmscan: remove memcg stalling on writeback pages during direct reclaim
Date: Mon, 23 Mar 2015 01:07:47 -0400 [thread overview]
Message-ID: <1427087267-16592-19-git-send-email-tj@kernel.org> (raw)
In-Reply-To: <1427087267-16592-1-git-send-email-tj@kernel.org>
Because writeback wasn't cgroup aware before, the usual dirty
throttling mechanism in balance_dirty_pages() didn't work for
processes under memcg limit. The writeback path didn't know how much
memory is available or how fast the dirty pages are being written out
for a given memcg and balance_dirty_pages() didn't have any measure of
IO back pressure for the memcg.
To work around the issue, memcg implemented an ad-hoc dirty throttling
mechanism in the direct reclaim path by stalling on pages under
writeback which are encountered during direct reclaim scan. This is
rather ugly and crude - none of the configurability, fairness, or
bandwidth-proportional distribution of the normal path.
The previous patches implemented proper memcg aware dirty throttling
and the ad-hoc mechanism is no longer necessary. Remove it.
Note: I removed the parts which seemed obvious and it behaves fine
while testing but my understanding of this code path is
rudimentary and it's quite possible that I got something wrong.
Please let me know if I got some wrong or more global_reclaim()
sites should be updated.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Vladimir Davydov <vdavydov@parallels.com>
---
mm/vmscan.c | 109 ++++++++++++++++++------------------------------------------
1 file changed, 33 insertions(+), 76 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 9f8d3c0..d084c95 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -929,53 +929,24 @@ static unsigned long shrink_page_list(struct list_head *page_list,
nr_congested++;
/*
- * If a page at the tail of the LRU is under writeback, there
- * are three cases to consider.
- *
- * 1) If reclaim is encountering an excessive number of pages
- * under writeback and this page is both under writeback and
- * PageReclaim then it indicates that pages are being queued
- * for IO but are being recycled through the LRU before the
- * IO can complete. Waiting on the page itself risks an
- * indefinite stall if it is impossible to writeback the
- * page due to IO error or disconnected storage so instead
- * note that the LRU is being scanned too quickly and the
- * caller can stall after page list has been processed.
- *
- * 2) Global reclaim encounters a page, memcg encounters a
- * page that is not marked for immediate reclaim or
- * the caller does not have __GFP_IO. In this case mark
- * the page for immediate reclaim and continue scanning.
- *
- * __GFP_IO is checked because a loop driver thread might
- * enter reclaim, and deadlock if it waits on a page for
- * which it is needed to do the write (loop masks off
- * __GFP_IO|__GFP_FS for this reason); but more thought
- * would probably show more reasons.
- *
- * Don't require __GFP_FS, since we're not going into the
- * FS, just waiting on its writeback completion. Worryingly,
- * ext4 gfs2 and xfs allocate pages with
- * grab_cache_page_write_begin(,,AOP_FLAG_NOFS), so testing
- * may_enter_fs here is liable to OOM on them.
- *
- * 3) memcg encounters a page that is not already marked
- * PageReclaim. memcg does not have any dirty pages
- * throttling so we could easily OOM just because too many
- * pages are in writeback and there is nothing else to
- * reclaim. Wait for the writeback to complete.
+ * A page at the tail of the LRU is under writeback. If
+ * reclaim is encountering an excessive number of pages
+ * under writeback and this page is both under writeback
+ * and PageReclaim then it indicates that pages are being
+ * queued for IO but are being recycled through the LRU
+ * before the IO can complete. Waiting on the page itself
+ * risks an indefinite stall if it is impossible to
+ * writeback the page due to IO error or disconnected
+ * storage so instead note that the LRU is being scanned
+ * too quickly and the caller can stall after page list has
+ * been processed.
*/
if (PageWriteback(page)) {
- /* Case 1 above */
if (current_is_kswapd() &&
PageReclaim(page) &&
test_bit(ZONE_WRITEBACK, &zone->flags)) {
nr_immediate++;
- goto keep_locked;
-
- /* Case 2 above */
- } else if (global_reclaim(sc) ||
- !PageReclaim(page) || !(sc->gfp_mask & __GFP_IO)) {
+ } else {
/*
* This is slightly racy - end_page_writeback()
* might have just cleared PageReclaim, then
@@ -989,13 +960,8 @@ static unsigned long shrink_page_list(struct list_head *page_list,
*/
SetPageReclaim(page);
nr_writeback++;
-
- goto keep_locked;
-
- /* Case 3 above */
- } else {
- wait_on_page_writeback(page);
}
+ goto keep_locked;
}
if (!force_reclaim)
@@ -1423,9 +1389,6 @@ static int too_many_isolated(struct zone *zone, int file,
if (current_is_kswapd())
return 0;
- if (!global_reclaim(sc))
- return 0;
-
if (file) {
inactive = zone_page_state(zone, NR_INACTIVE_FILE);
isolated = zone_page_state(zone, NR_ISOLATED_FILE);
@@ -1615,35 +1578,29 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
set_bit(ZONE_WRITEBACK, &zone->flags);
/*
- * memcg will stall in page writeback so only consider forcibly
- * stalling for global reclaim
+ * Tag a zone as congested if all the dirty pages scanned were
+ * backed by a congested BDI and wait_iff_congested will stall.
*/
- if (global_reclaim(sc)) {
- /*
- * Tag a zone as congested if all the dirty pages scanned were
- * backed by a congested BDI and wait_iff_congested will stall.
- */
- if (nr_dirty && nr_dirty == nr_congested)
- set_bit(ZONE_CONGESTED, &zone->flags);
+ if (nr_dirty && nr_dirty == nr_congested)
+ set_bit(ZONE_CONGESTED, &zone->flags);
- /*
- * If dirty pages are scanned that are not queued for IO, it
- * implies that flushers are not keeping up. In this case, flag
- * the zone ZONE_DIRTY and kswapd will start writing pages from
- * reclaim context.
- */
- if (nr_unqueued_dirty == nr_taken)
- set_bit(ZONE_DIRTY, &zone->flags);
+ /*
+ * If dirty pages are scanned that are not queued for IO, it
+ * implies that flushers are not keeping up. In this case, flag the
+ * zone ZONE_DIRTY and kswapd will start writing pages from reclaim
+ * context.
+ */
+ if (nr_unqueued_dirty == nr_taken)
+ set_bit(ZONE_DIRTY, &zone->flags);
- /*
- * If kswapd scans pages marked marked for immediate
- * reclaim and under writeback (nr_immediate), it implies
- * that pages are cycling through the LRU faster than
- * they are written so also forcibly stall.
- */
- if (nr_immediate && current_may_throttle())
- congestion_wait(BLK_RW_ASYNC, HZ/10);
- }
+ /*
+ * If kswapd scans pages marked marked for immediate reclaim and
+ * under writeback (nr_immediate), it implies that pages are
+ * cycling through the LRU faster than they are written so also
+ * forcibly stall.
+ */
+ if (nr_immediate && current_may_throttle())
+ congestion_wait(BLK_RW_ASYNC, HZ/10);
/*
* Stall direct reclaim for IO completions if underlying BDIs or zone
--
2.1.0
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2015-03-23 5:08 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-23 5:07 [PATCHSET 2/3 block/for-4.1/core] writeback: cgroup writeback backpressure propagation Tejun Heo
2015-03-23 5:07 ` [PATCH 01/18] memcg: make mem_cgroup_read_{stat|event}() iterate possible cpus instead of online Tejun Heo
2015-03-25 22:39 ` [PATCH 1.5/18] writeback: clean up wb_dirty_limit() Tejun Heo
2015-03-23 5:07 ` [PATCH 02/18] writeback: reorganize [__]wb_update_bandwidth() Tejun Heo
2015-03-23 5:07 ` [PATCH 03/18] writeback: implement wb_domain Tejun Heo
2015-03-23 5:07 ` [PATCH 04/18] writeback: move global_dirty_limit into wb_domain Tejun Heo
2015-03-23 5:07 ` [PATCH 05/18] writeback: consolidate dirty throttle parameters into dirty_throttle_control Tejun Heo
2015-03-23 5:07 ` [PATCH 06/18] writeback: add dirty_throttle_control->wb_bg_thresh Tejun Heo
2015-03-23 5:07 ` [PATCH 07/18] writeback: make __wb_dirty_limit() take dirty_throttle_control Tejun Heo
2015-03-25 22:42 ` [PATCH v2 07/18] writeback: make __wb_calc_thresh() " Tejun Heo
2015-03-23 5:07 ` [PATCH 08/18] writeback: add dirty_throttle_control->pos_ratio Tejun Heo
2015-03-23 5:07 ` [PATCH 09/18] writeback: add dirty_throttle_control->wb_completions Tejun Heo
2015-03-23 5:07 ` [PATCH 10/18] writeback: add dirty_throttle_control->dom Tejun Heo
2015-03-23 5:07 ` [PATCH 11/18] writeback: make __wb_writeout_inc() and hard_dirty_limit() take wb_domaas a parameter Tejun Heo
2015-03-23 5:07 ` [PATCH 12/18] writeback: separate out domain_dirty_limits() Tejun Heo
2015-03-23 5:07 ` [PATCH 13/18] writeback: move over_bground_thresh() to mm/page-writeback.c Tejun Heo
2015-03-23 5:07 ` [PATCH 14/18] writeback: update wb_over_bg_thresh() to use wb_domain aware operations Tejun Heo
2015-03-23 5:07 ` [PATCH 15/18] writeback: implement memcg wb_domain Tejun Heo
2015-03-23 5:07 ` [PATCH 16/18] writeback: reset wb_domain->dirty_limit[_tstmp] when memcg domain size changes Tejun Heo
2015-03-23 5:07 ` [PATCH 17/18] writeback: implement memcg writeback domain based throttling Tejun Heo
2015-03-23 5:07 ` Tejun Heo [this message]
2015-03-23 5:27 ` [PATCH 18/18] mm: vmscan: remove memcg stalling on writeback pages during direct reclaim Tejun Heo
2015-03-25 22:26 ` [PATCH v2 18/18] mm: vmscan: disable memcg direct reclaim stalling if cgroup writeback support is in use Tejun Heo
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1427087267-16592-19-git-send-email-tj@kernel.org \
--to=tj@kernel.org \
--cc=axboe@kernel.dk \
--cc=cgroups@vger.kernel.org \
--cc=clm@fb.com \
--cc=david@fromorbit.com \
--cc=fengguang.wu@intel.com \
--cc=gthelen@google.com \
--cc=hannes@cmpxchg.org \
--cc=hch@infradead.org \
--cc=jack@suse.cz \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=lizefan@huawei.com \
--cc=mhocko@suse.cz \
--cc=vdavydov@parallels.com \
--cc=vgoyal@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).