The patch titled Subject: mm: fix calculation of dirtyable memory has been removed from the -mm tree. Its filename was mm-fix-calculation-of-dirtyable-memory.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: Sonny Rao <sonnyrao@xxxxxxxxxxxx> Subject: mm: fix calculation of dirtyable memory The system uses global_dirtyable_memory() to calculate number of dirtyable pages/pages that can be allocated to the page cache. A bug causes an underflow thus making the page count look like a big unsigned number. This in turn confuses the dirty writeback throttling to aggressively write back pages as they become dirty (usually 1 page at a time). This generally only affects systems with highmem because the underflowed count gets subtracted from the global count of dirtyable memory. The problem was introduced with v3.2-4896-gab8fabd Fix is to ensure we don't get an underflowed total of either highmem or global dirtyable memory. Signed-off-by: Sonny Rao <sonnyrao@xxxxxxxxxxxx> Signed-off-by: Puneet Kumar <puneetster@xxxxxxxxxxxx> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> Tested-by: Damien Wyart <damien.wyart@xxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/page-writeback.c | 25 ++++++++++++++++++++----- 1 file changed, 20 insertions(+), 5 deletions(-) diff -puN mm/page-writeback.c~mm-fix-calculation-of-dirtyable-memory mm/page-writeback.c --- a/mm/page-writeback.c~mm-fix-calculation-of-dirtyable-memory +++ a/mm/page-writeback.c @@ -201,6 +201,18 @@ static unsigned long highmem_dirtyable_m zone_reclaimable_pages(z) - z->dirty_balance_reserve; } /* + * Unreclaimable memory (kernel memory or anonymous memory + * without swap) can bring down the dirtyable pages below + * the zone's dirty balance reserve and the above calculation + * will underflow. However we still want to add in nodes + * which are below threshold (negative values) to get a more + * accurate calculation but make sure that the total never + * underflows. + */ + if ((long)x < 0) + x = 0; + + /* * Make sure that the number of highmem pages is never larger * than the number of the total dirtyable memory. This can only * occur in very strange VM situations but we want to make sure @@ -222,8 +234,8 @@ static unsigned long global_dirtyable_me { unsigned long x; - x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages() - - dirty_balance_reserve; + x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages(); + x -= min(x, dirty_balance_reserve); if (!vm_highmem_is_dirtyable) x -= highmem_dirtyable_memory(x); @@ -290,9 +302,12 @@ static unsigned long zone_dirtyable_memo * highmem zone can hold its share of dirty pages, so we don't * care about vm_highmem_is_dirtyable here. */ - return zone_page_state(zone, NR_FREE_PAGES) + - zone_reclaimable_pages(zone) - - zone->dirty_balance_reserve; + unsigned long nr_pages = zone_page_state(zone, NR_FREE_PAGES) + + zone_reclaimable_pages(zone); + + /* don't allow this to underflow */ + nr_pages -= min(nr_pages, zone->dirty_balance_reserve); + return nr_pages; } /** _ Patches currently in -mm which might be from sonnyrao@xxxxxxxxxxxx are origin.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html