On 03/09/2015 04:48 PM, Eric B Munson wrote:
Currently, pages which are marked as unevictable are protected from compaction, but not from other types of migration. The mlock desctription does not promise that all page faults will be avoided, only major ones so this protection is not necessary. This extra protection can cause problems for applications that are using mlock to avoid swapping pages out, but require order > 0 allocations to continue to succeed in a fragmented environment. This patch removes the ISOLATE_UNEVICTABLE mode and the check for it in __isolate_lru_page(). Removing this check allows the removal of the isolate_mode argument from isolate_migratepages_block() because it can compute the required mode from the compact_control structure. To illustrate this problem I wrote a quick test program that mmaps a large number of 1MB files filled with random data. These maps are created locked and read only. Then every other mmap is unmapped and I attempt to allocate huge pages to the static huge page pool. Without this patch I am unable to allocate any huge pages after fragmenting memory. With it, I can allocate almost all the space freed by unmapping as huge pages. Signed-off-by: Eric B Munson <emunson@xxxxxxxxxx> Acked-by: David Rientjes <rientjes@xxxxxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Christoph Lameter <cl@xxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: linux-mm@xxxxxxxxx Cc: linux-kernel@xxxxxxxxxxxxxxx
Acked-by: Rik van Riel <riel@xxxxxxxxxx> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>