On 01/13/2017 12:51 PM, Lucas Stach wrote:
Commit 73e64c51afc5 (mm, compaction: allow compaction for GFP_NOFS requests)
changed compation to skip FS pages if not explicitly allowed to touch them,
but missed to update the CMA compact_control.
This leads to a very high isolation failure rate, crippling performance of
CMA even on a lightly loaded system. Re-allow CMA to compact FS pages by
setting the correct GFP flags, restoring CMA behavior and performance to
the kernel 4.9 level.
Fixes: 73e64c51afc5 (mm, compaction: allow compaction for GFP_NOFS requests)
Signed-off-by: Lucas Stach <l.stach@xxxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
It's true that this restores the behavior for CMA to 4.9. But it also reveals
that CMA always implicitly assumed to be called from non-fs context. That's
expectable for the original CMA use-case of drivers for devices such as cameras,
but I now wonder if there's danger when CMA gets invoked via dma-cma layer with
generic cma range for e.g. a disk device... I guess that would be another
argument for scoped GFP_NOFS, which should then be applied to adjust the
gfp_mask here. Or we could apply at least memalloc_noio_flags() right now, which
should already handle the disk device -> dma -> cma scenario?
---
mm/page_alloc.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8d5d82c8a85a..eced9fee582b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7255,6 +7255,7 @@ int alloc_contig_range(unsigned long start, unsigned long end,
.zone = page_zone(pfn_to_page(start)),
.mode = MIGRATE_SYNC,
.ignore_skip_hint = true,
+ .gfp_mask = GFP_KERNEL,
};
INIT_LIST_HEAD(&cc.migratepages);
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