Eric Lee / linux-smarc-t335x-v3.2

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Commit 82478fb7bca28e3ca2f3c55c14e690f749dd4dbb

Authored by Johannes Weiner
Committed by Linus Torvalds
1 parent 3305de51bf
Exists in master and in 4 other branches v3.2_AM335xPSP_04.06.00.11, v3.2_NEWT335xPSP_04.06.00.11, v3.2_SBC_SMARTMEN, v3.2_SMARCT335xPSP_04.06.00.11

mm: compaction: prevent division-by-zero during user-requested compaction 

Up until 3e7d344 ("mm: vmscan: reclaim order-0 and use compaction instead
of lumpy reclaim"), compaction skipped calculating the fragmentation index
of a zone when compaction was explicitely requested through the procfs
knob.

However, when compaction_suitable was introduced, it did not come with an
extra check for order == -1, set on explicit compaction requests, and
passed this order on to the fragmentation index calculation, where it
overshifts the number of requested pages, leading to a division by zero.

This patch makes sure that order == -1 is recognized as the flag it is
rather than passing it along as valid order parameter.

[akpm@linux-foundation.org: add comment, per Mel]
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Showing 1 changed file with 11 additions and 0 deletions Side-by-side Diff

... ... @@ -406,6 +406,10 @@
406 406 if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
407 407 return COMPACT_CONTINUE;
408 408  
  409 + /*
  410 + * order == -1 is expected when compacting via
  411 + * /proc/sys/vm/compact_memory
  412 + */
409 413 if (cc->order == -1)
410 414 return COMPACT_CONTINUE;
411 415  
... ... @@ -452,6 +456,13 @@
452 456 watermark = low_wmark_pages(zone) + (2UL << order);
453 457 if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
454 458 return COMPACT_SKIPPED;
  459 +
  460 + /*
  461 + * order == -1 is expected when compacting via
  462 + * /proc/sys/vm/compact_memory
  463 + */
  464 + if (order == -1)
  465 + return COMPACT_CONTINUE;
455 466  
456 467 /*
457 468 * fragmentation index determines if allocation failures are due to