From: Michal Hocko <mhocko@xxxxxxxx> Subject: 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@xxxxxxxxxxxxxxxxxxxx: coding-style fixes] Link: http://lkml.kernel.org/r/20170517080932.21423-1-mhocko@xxxxxxxxxx Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> Suggested-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/util.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff -puN mm/util.c~mm-clarify-why-we-want-kmalloc-before-falling-backto-vmallock mm/util.c --- a/mm/util.c~mm-clarify-why-we-want-kmalloc-before-falling-backto-vmallock +++ a/mm/util.c @@ -357,8 +357,11 @@ void *kvmalloc_node(size_t size, gfp_t f 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; _ -- 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
