mm, page_alloc: Always use a captured page regardless of compaction result
Subsystems (2)
PATCH 1/1 mm, page_alloc: Always use a captured page regardless of compaction result
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.
--- mm/page_alloc.c | 5 ----- 1 file changed, 5 deletions(-)
mm/page_alloc.c +0 -5
@@ -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
Quoted 22 lines · Mel Gorman
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
Quoted 8 lines
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 <[email protected]>Signed-off-by Mel Gorman <[email protected]>
Ah, noticed the new formal resend only after replying to the first one, so here goes again:
Yup, no need for a Cc: stable on a very rare WARN_ON_ONCE. So the AI will pick it anyway...
Quoted 21 lines
--- mm/page_alloc.c | 5 ----- 1 file changed, 5 deletions(-)mm/page_alloc.c +0
-5@@ -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
Quoted 32 lines · Vlastimil Babka
Quoted 22 lines · Mel Gorman
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 #1Quoted 8 lines
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 <[email protected]>Signed-off-by Mel Gorman <[email protected]>
Quoted 8 lines
Ah, noticed the new formal resend only after replying to the first one, so here goes again:
Yup, no need for a Cc: stable on a very rare
WARN_ON_ONCE. So the AI will pick it anyway...Acked-by Vlastimil Babka <[email protected]>
With luck, this will be picked up and sent to Linus before 5.1 releases and then the stable bot will not need to touch the commit at all.
Signature · 2 lines
Mel Gorman SUSE Labs