+ mm-page_alloc-always-use-a-captured-page-regardless-of-compaction-result.patch added to -mm tree

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



The patch titled
     Subject: mm, page_alloc: always use a captured page regardless of compaction result
has been added to the -mm tree.  Its filename is
     mm-page_alloc-always-use-a-captured-page-regardless-of-compaction-result.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/mm-page_alloc-always-use-a-captured-page-regardless-of-compaction-result.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/mm-page_alloc-always-use-a-captured-page-regardless-of-compaction-result.patch

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next and is updated
there every 3-4 working days

------------------------------------------------------
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
_

Patches currently in -mm which might be from mgorman@xxxxxxxxxxxxxxxxxxx are

mm-do-not-boost-watermarks-to-avoid-fragmentation-for-the-discontig-memory-model.patch
mm-page_alloc-always-use-a-captured-page-regardless-of-compaction-result.patch




[Index of Archives]     [Kernel Archive]     [IETF Annouce]     [DCCP]     [Netdev]     [Networking]     [Security]     [Bugtraq]     [Yosemite]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Linux SCSI]

  Powered by Linux