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authorMichal Hocko <mhocko@suse.com>2017-06-02 14:46:19 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-06-02 15:07:37 -0700
commit4f4f2ba9c531b3d7cee293dd3654ba3b86e7d220 (patch)
treee76d33e876e50dcbeb4dc88a919003657911b785
parent60b0a8c3d2480f3b57282b47b7cae7ee71c48635 (diff)
downloadleg-kernel-4f4f2ba9c531b3d7cee293dd3654ba3b86e7d220.tar.gz
mm: clarify why we want kmalloc before falling backto vmallock
While converting drm_[cm]alloc* helpers to kvmalloc* variants Chris Wilson has wondered why we want to try kmalloc before vmalloc fallback even for larger allocations requests. Let's clarify that one larger physically contiguous block is less likely to fragment memory than many scattered pages which can prevent more large blocks from being created. [akpm@linux-foundation.org: coding-style fixes] Link: http://lkml.kernel.org/r/20170517080932.21423-1-mhocko@kernel.org Signed-off-by: Michal Hocko <mhocko@suse.com> Suggested-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> Acked-by: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/util.c7
1 files changed, 5 insertions, 2 deletions
diff --git a/mm/util.c b/mm/util.c
index 464df3489903..26be6407abd7 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -357,8 +357,11 @@ void *kvmalloc_node(size_t size, gfp_t flags, int node)
WARN_ON_ONCE((flags & GFP_KERNEL) != GFP_KERNEL);
/*
- * Make sure that larger requests are not too disruptive - no OOM
- * killer and no allocation failure warnings as we have a fallback
+ * We want to attempt a large physically contiguous block first because
+ * it is less likely to fragment multiple larger blocks and therefore
+ * contribute to a long term fragmentation less than vmalloc fallback.
+ * However make sure that larger requests are not too disruptive - no
+ * OOM killer and no allocation failure warnings as we have a fallback.
*/
if (size > PAGE_SIZE) {
kmalloc_flags |= __GFP_NOWARN;