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From: Mel Gorman <>
To: Andrew Morton <>
Cc: Li Wang <>, Vlastimil Babka <>,
	linux-mm <>,
Subject: [PATCH] mm, page_alloc: Always use a captured page regardless of compaction result
Date: Fri, 19 Apr 2019 09:51:33 +0100
Message-ID: <> (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: 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()

Fixes: 5e1f0f098b46 ("mm, compaction: capture a page under direct compaction")
Reported-by: Li Wang <>
Signed-off-by: Mel Gorman <>
 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,
-	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

             reply index

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 ` Vlastimil Babka
2019-04-19 13:30   ` Mel Gorman

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