Patch "mm, compaction: prevent VM_BUG_ON when terminating freeing scanner" has been added to the 4.6-stable tree
Subsystems (3)
This is a note to let you know that I've just added the patch titled
mm, compaction: prevent VM_BUG_ON when terminating freeing scanner
to the 4.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-compaction-prevent-vm_bug_on-when-terminating-freeing-scanner.patch
and it can be found in the queue-4.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.
Quoted 1 line
From
a46cbf3bc53b6a93fb84a5ffb288c354fa807954Mon Sep 17 00:00:00 2001
From: David Rientjes <[email protected]>
Date: Thu, 14 Jul 2016 12:06:50 -0700
Subject: mm, compaction: prevent VM_BUG_ON when terminating freeing scanner
From: David Rientjes <[email protected]>
commit a46cbf3bc53b6a93fb84a5ffb288c354fa807954 upstream.
It's possible to isolate some freepages in a pageblock and then fail split_free_page() due to the low watermark check. In this case, we hit VM_BUG_ON() because the freeing scanner terminated early without a contended lock or enough freepages.
This should never have been a VM_BUG_ON() since it's not a fatal condition. It should have been a VM_WARN_ON() at best, or even handled gracefully.
Regardless, we need to terminate anytime the full pageblock scan was not done. The logic belongs in isolate_freepages_block(), so handle its state gracefully by terminating the pageblock loop and making a note to restart at the same pageblock next time since it was not possible to complete the scan this time.
--- mm/compaction.c | 36 ++++++++++++++---------------------- 1 file changed, 14 insertions(+), 22 deletions(-)
mm/compaction.c +14 -22
@@ -936,8 +936,6 @@ static void isolate_freepages(struct com block_end_pfn = block_start_pfn, block_start_pfn -= pageblock_nr_pages, isolate_start_pfn = block_start_pfn) { -unsigned long isolated; -/* * This can iterate a massively long zone without finding any * suitable migration targets, so periodically check if we need
@@ -961,36 +959,30 @@ static void isolate_freepages(struct comcontinue ;/* Found a block suitable for isolating free pages from. */ - isolated =isolate_freepages_block (cc, &isolate_start_pfn, - block_end_pfn, freelist, false); -/* If isolation failed early, do not continue needlessly */ -if (!isolated && isolate_start_pfn < block_end_pfn && - cc->nr_migratepages > cc->nr_freepages) -break ; +isolate_freepages_block (cc, &isolate_start_pfn, block_end_pfn, + freelist, false);/* -* If we isolated enough freepages, or aborted due to async -* compaction being contended, terminate the loop. -* Remember where the free scanner should restart next time, -* which is where isolate_freepages_block() left off. -* But if it scanned the whole pageblock, isolate_start_pfn -* now points at block_end_pfn, which is the start of the next -* pageblock. -* In that case we will however want to restart at the start -* of the previous pageblock. +* If we isolated enough freepages, or aborted due to lock +* contention, terminate. */ if ((cc->nr_freepages >= cc->nr_migratepages) || cc->contended) { -if (isolate_start_pfn >= block_end_pfn) +if (isolate_start_pfn >= block_end_pfn) { +/* +* Restart at previous pageblock if more +* freepages can be isolated next time. +*/ isolate_start_pfn = block_start_pfn - pageblock_nr_pages; + }break ; - }else { + }else if (isolate_start_pfn < block_end_pfn) {/* -* isolate_freepages_block() should not terminate -* prematurely unless contended, or isolated enough +* If isolation failed early, do not continue +* needlessly. */ -VM_BUG_ON (isolate_start_pfn < block_end_pfn); +break ; } }
Patches currently in stable-queue which might be from [email protected] are
queue-4.6/mm-compaction-abort-free-scanner-if-split-fails.patch queue-4.6/mm-compaction-prevent-vm_bug_on-when-terminating-freeing-scanner.patch queue-4.6/mm-meminit-always-return-a-valid-node-from-early_pfn_to_nid.patch queue-4.6/mm-meminit-ensure-node-is-online-before-checking-whether-pages-are-uninitialised.patch