From: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Subject: mm, page_alloc: always use a captured page regardless of compaction result
During the development of 5e1f0f098b46 ("mm, compaction: capture a page
under direct compaction"), a paranoid check was added to ensure that if a
captured page was available after compaction that it was consistent with
the final state of compaction. The intent was to catch serious
programming bugs such as using a stale page pointer and causing corruption
problems.
However, it is possible to get a captured page even if compaction was
unsuccessful if an interrupt triggered and happened to free pages in
interrupt context that got merged into a suitable high-order page. It's
highly unlikely but Li Wang did report the following warning on s390
occuring when testing OOM handling. Note that the warning is slightly
edited for clarity.
[ 1422.124060] WARNING: CPU: 0 PID: 9783 at mm/page_alloc.c:3777 __alloc_pages_direct_compact+0x182/0x190
[ 1422.124065] Modules linked in: rpcsec_gss_krb5 auth_rpcgss nfsv4 dns_resolver
nfs lockd grace fscache sunrpc pkey ghash_s390 prng xts aes_s390 des_s390
des_generic sha512_s390 zcrypt_cex4 zcrypt vmur binfmt_misc ip_tables xfs
libcrc32c dasd_fba_mod qeth_l2 dasd_eckd_mod dasd_mod qeth qdio lcs ctcm
ccwgroup fsm dm_mirror dm_region_hash dm_log dm_mod
[ 1422.124086] CPU: 0 PID: 9783 Comm: copy.sh Kdump: loaded Not tainted 5.1.0-rc 5 #1
This patch simply removes the check entirely instead of trying to be
clever about pages freed from interrupt context. If a serious programming
error was introduced, it is highly likely to be caught by prep_new_page()
instead.
Link: http://lkml.kernel.org/r/20190419085133.GH18914@xxxxxxxxxxxxxxxxxxx
Fixes: 5e1f0f098b46 ("mm, compaction: capture a page under direct compaction")
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Reported-by: Li Wang <liwang@xxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 5 -----
1 file changed, 5 deletions(-)
--- a/mm/page_alloc.c~mm-page_alloc-always-use-a-captured-page-regardless-of-compaction-result
+++ a/mm/page_alloc.c
@@ -3786,11 +3786,6 @@ __alloc_pages_direct_compact(gfp_t gfp_m
memalloc_noreclaim_restore(noreclaim_flag);
psi_memstall_leave(&pflags);
- if (*compact_result <= COMPACT_INACTIVE) {
- WARN_ON_ONCE(page);
- return NULL;
- }
-
/*
* At least in one zone compaction wasn't deferred or skipped, so let's
* count a compaction stall
_
