On Tue, Nov 11, 2014 at 05:56:03PM -0800, Andrew Morton wrote:
On Wed, 12 Nov 2014 03:47:03 +0200 "Kirill A. Shutemov" kirill@shutemov.name wrote:
On Wed, Nov 12, 2014 at 03:22:41AM +0200, Kirill A. Shutemov wrote:
On Tue, Nov 11, 2014 at 04:49:13PM -0800, Andrew Morton wrote:
On Tue, 11 Nov 2014 18:36:28 -0600 (CST) Christoph Lameter cl@linux.com wrote:
On Tue, 11 Nov 2014, Andrew Morton wrote:
There's no point in doing
#define GFP_SLAB_BUG_MASK (__GFP_DMA32|__GFP_HIGHMEM|~__GFP_BITS_MASK)
because __GFP_DMA32|__GFP_HIGHMEM are already part of ~__GFP_BITS_MASK.
?? ~__GFP_BITS_MASK means bits 25 to 31 are set.
__GFP_DMA32 is bit 2 and __GFP_HIGHMEM is bit 1.
Ah, yes, OK.
I suppose it's possible that __GFP_HIGHMEM was set.
do_huge_pmd_anonymous_page ->pte_alloc_one ->alloc_pages(__userpte_alloc_gfp==__GFP_HIGHMEM)
do_huge_pmd_anonymous_page alloc_hugepage_vma alloc_pages_vma(GFP_TRANSHUGE)
GFP_TRANSHUGE contains GFP_HIGHUSER_MOVABLE, which has __GFP_HIGHMEM.
Looks like it's reasonable to sanitize flags in shrink_slab() by dropping flags incompatible with slab expectation. Like this:
diff --git a/mm/vmscan.c b/mm/vmscan.c index dcb47074ae03..eb165d29c5e5 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -369,6 +369,8 @@ unsigned long shrink_slab(struct shrink_control *shrinkctl, if (nr_pages_scanned == 0) nr_pages_scanned = SWAP_CLUSTER_MAX;
shrinkctl->gfp_mask &= ~(__GFP_DMA32 | __GFP_HIGHMEM);if (!down_read_trylock(&shrinker_rwsem)) { /* * If we would return 0, our callers would understand that weWell no, because nobody is supposed to be passing this gfp_mask back into a new allocation attempt anyway. It would be better to do
shrinkctl->gfp_mask |= __GFP_IMMEDIATELY_GO_BUG;
?
From my POV, the problem is that we combine what-need-to-be-freed gfp_mask
with if-have-to-allocate gfp_mask: we want to respect __GFP_IO/FS on alloc, but not nessesary both if there's no restriction from the context.
For shrink_slab(), __GFP_DMA32 and __GFP_HIGHMEM don't make sense in both cases.
__GFP_IMMEDIATELY_GO_BUG would work too, but we also need to provide macros to construct alloc-suitable mask from the given one for yes-i-really-have-to-allocate case.