From: Vlastimil Babka <vbabka@xxxxxxx> Subject: mm, mempolicy: don't check cpuset seqlock where it doesn't matter Two wrappers of __alloc_pages_nodemask() are checking task->mems_allowed_seq themselves to retry allocation that has raced with a cpuset update. This has been shown to be ineffective in preventing premature OOM's which can happen in __alloc_pages_slowpath() long before it returns back to the wrappers to detect the race at that level. Previous patches have made __alloc_pages_slowpath() more robust, so we can now simply remove the seqlock checking in the wrappers to prevent further wrong impression that it can actually help. Link: http://lkml.kernel.org/r/20170517081140.30654-7-vbabka@xxxxxxx Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Anshuman Khandual <khandual@xxxxxxxxxxxxxxxxxx> Cc: Christoph Lameter <cl@xxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Dimitri Sivanich <sivanich@xxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Li Zefan <lizefan@xxxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/mempolicy.c | 16 ---------------- 1 file changed, 16 deletions(-) diff -puN mm/mempolicy.c~mm-mempolicy-dont-check-cpuset-seqlock-where-it-doesnt-matter mm/mempolicy.c --- a/mm/mempolicy.c~mm-mempolicy-dont-check-cpuset-seqlock-where-it-doesnt-matter +++ a/mm/mempolicy.c @@ -1898,12 +1898,9 @@ alloc_pages_vma(gfp_t gfp, int order, st struct mempolicy *pol; struct page *page; int preferred_nid; - unsigned int cpuset_mems_cookie; nodemask_t *nmask; -retry_cpuset: pol = get_vma_policy(vma, addr); - cpuset_mems_cookie = read_mems_allowed_begin(); if (pol->mode == MPOL_INTERLEAVE) { unsigned nid; @@ -1945,8 +1942,6 @@ retry_cpuset: page = __alloc_pages_nodemask(gfp, order, preferred_nid, nmask); mpol_cond_put(pol); out: - if (unlikely(!page && read_mems_allowed_retry(cpuset_mems_cookie))) - goto retry_cpuset; return page; } @@ -1964,23 +1959,15 @@ out: * Allocate a page from the kernel page pool. When not in * interrupt context and apply the current process NUMA policy. * Returns NULL when no page can be allocated. - * - * Don't call cpuset_update_task_memory_state() unless - * 1) it's ok to take cpuset_sem (can WAIT), and - * 2) allocating for current task (not interrupt). */ struct page *alloc_pages_current(gfp_t gfp, unsigned order) { struct mempolicy *pol = &default_policy; struct page *page; - unsigned int cpuset_mems_cookie; if (!in_interrupt() && !(gfp & __GFP_THISNODE)) pol = get_task_policy(current); -retry_cpuset: - cpuset_mems_cookie = read_mems_allowed_begin(); - /* * No reference counting needed for current->mempolicy * nor system default_policy @@ -1992,9 +1979,6 @@ retry_cpuset: policy_node(gfp, pol, numa_node_id()), policy_nodemask(gfp, pol)); - if (unlikely(!page && read_mems_allowed_retry(cpuset_mems_cookie))) - goto retry_cpuset; - return page; } EXPORT_SYMBOL(alloc_pages_current); _ -- 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
