Message-Id: <20240821135900.2199983-1-hezhongkun.hzk@bytedance.com>
Date: Wed, 21 Aug 2024 21:59:00 +0800
From: Zhongkun He <hezhongkun.hzk@...edance.com>
To: mhocko@...e.com,
	akpm@...ux-foundation.org,
	mgorman@...hsingularity.net,
	hannes@...xchg.org
Cc: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	lizefan.x@...edance.com,
	Zhongkun He <hezhongkun.hzk@...edance.com>
Subject: [PATCH] mm:page_alloc: fix the NULL ac->nodemask in __alloc_pages_slowpath()

I found a problem in my test machine that should_reclaim_retry() do
not get the right node if i set the cpuset.mems

1.Test step and the machines.
------------
root@vm:/sys/fs/cgroup/test# numactl -H | grep size
node 0 size: 9477 MB
node 1 size: 10079 MB
node 2 size: 10079 MB
node 3 size: 10078 MB

root@vm:/sys/fs/cgroup/test# cat cpuset.mems
    2

root@vm:/sys/fs/cgroup/test# stress --vm 1 --vm-bytes 12g  --vm-keep
stress: info: [33430] dispatching hogs: 0 cpu, 0 io, 1 vm, 0 hdd
stress: FAIL: [33430] (425) <-- worker 33431 got signal 9
stress: WARN: [33430] (427) now reaping child worker processes
stress: FAIL: [33430] (461) failed run completed in 2s

2. reclaim_retry_zone info:

We can only alloc pages from node=2, but the reclaim_retry_zone is
node=0 and return true.

root@vm:/sys/kernel/debug/tracing# cat trace
stress-33431   [001] ..... 13223.617311: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=1 wmark_check=1
stress-33431   [001] ..... 13223.617682: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=2 wmark_check=1
stress-33431   [001] ..... 13223.618103: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=3 wmark_check=1
stress-33431   [001] ..... 13223.618454: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=4 wmark_check=1
stress-33431   [001] ..... 13223.618770: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=5 wmark_check=1
stress-33431   [001] ..... 13223.619150: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=6 wmark_check=1
stress-33431   [001] ..... 13223.619510: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=7 wmark_check=1
stress-33431   [001] ..... 13223.619850: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=8 wmark_check=1
stress-33431   [001] ..... 13223.620171: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=9 wmark_check=1
stress-33431   [001] ..... 13223.620533: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=10 wmark_check=1
stress-33431   [001] ..... 13223.620894: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=11 wmark_check=1
stress-33431   [001] ..... 13223.621224: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=12 wmark_check=1
stress-33431   [001] ..... 13223.621551: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=13 wmark_check=1
stress-33431   [001] ..... 13223.621847: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=14 wmark_check=1
stress-33431   [001] ..... 13223.622200: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=15 wmark_check=1
stress-33431   [001] ..... 13223.622580: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=16 wmark_check=1

3. Root cause:
Nodemask usually comes from mempolicy in policy_nodemask(), which
is always NULL unless the memory policy is bind or prefer_many.

nodemask = NULL
__alloc_pages_noprof()
	prepare_alloc_pages
		ac->nodemask = &cpuset_current_mems_allowed;

	get_page_from_freelist()

	ac.nodemask = nodemask;  /*set  NULL*/

	__alloc_pages_slowpath() {
		f (!(alloc_flags & ALLOC_CPUSET) || reserve_flags) {
			ac->nodemask = NULL;
			ac->preferred_zoneref = first_zones_zonelist(ac->zonelist,
					ac->highest_zoneidx, ac->nodemask);

		/* so ac.nodemask = NULL */
	}

According to the function flow above, we do not have the memory limit to
follow cpuset.mems, so we need to add it.

Test result:
Try 3 times with different cpuset.mems and alloc large memorys than that numa size.
echo 1 > cpuset.mems
stress --vm 1 --vm-bytes 12g --vm-hang 0
---------------
echo 2 > cpuset.mems
stress --vm 1 --vm-bytes 12g --vm-hang 0
---------------
echo 3 > cpuset.mems
stress --vm 1 --vm-bytes 12g --vm-hang 0

The retry trace look like:
stress-2139    [003] .....   666.934104: reclaim_retry_zone: node=1 zone=Normal   order=0 reclaimable=7 available=7355 min_wmark=8598 no_progress_loops=1 wmark_check=0
stress-2204    [010] .....   695.447393: reclaim_retry_zone: node=2 zone=Normal   order=0 reclaimable=2 available=6916 min_wmark=8598 no_progress_loops=1 wmark_check=0
stress-2271    [008] .....   725.683058: reclaim_retry_zone: node=3 zone=Normal   order=0 reclaimable=17 available=8079 min_wmark=8597 no_progress_loops=1 wmark_check=0

With this patch, we can check the right node and get less retry in __alloc_pages_slowpath()
because there is nothing to do.

Signed-off-by: Zhongkun He <hezhongkun.hzk@...edance.com>
---
 mm/page_alloc.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 29608ca294cf..5ea63bb8f8ff 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4338,6 +4338,9 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 		ac->nodemask = NULL;
 		ac->preferred_zoneref = first_zones_zonelist(ac->zonelist,
 					ac->highest_zoneidx, ac->nodemask);
+	} else if (in_task() && !ac->nodemask) {
+		/* Set the nodemask if the request comes from user space. */
+		ac->nodemask = &cpuset_current_mems_allowed;
 	}
 
 	/* Attempt with potentially adjusted zonelist and alloc_flags */
-- 
2.20.1

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