From: Mel Gorman <mgorman@techsingularity.net>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Li Wang <liwang@redhat.com>, Vlastimil Babka <vbabka@suse.cz>,
linux-mm <linux-mm@kvack.org>,
linux-kernel@vger.kernel.org
Subject: [PATCH] mm, page_alloc: Always use a captured page regardless of compaction result
Date: Fri, 19 Apr 2019 09:51:33 +0100 [thread overview]
Message-ID: <20190419085133.GH18914@techsingularity.net> (raw)
During the development of commit 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.
Fixes: 5e1f0f098b46 ("mm, compaction: capture a page under direct compaction")
Reported-by: Li Wang <liwang@redhat.com>
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
mm/page_alloc.c | 5 -----
1 file changed, 5 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d96ca5bc555b..cfaba3889fa2 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3773,11 +3773,6 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
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
next reply other threads:[~2019-04-19 8:51 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-19 8:51 Mel Gorman [this message]
2019-04-19 12:54 ` [PATCH] mm, page_alloc: Always use a captured page regardless of compaction result Vlastimil Babka
2019-04-19 13:30 ` Mel Gorman
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