From bf14ed81f571f8dba31cd72ab2e50fbcc877cc31 Mon Sep 17 00:00:00 2001 From: yangge Date: Thu, 20 Jun 2024 08:59:50 +0800 Subject: mm/page_alloc: Separate THP PCP into movable and non-movable categories Since commit 5d0a661d808f ("mm/page_alloc: use only one PCP list for THP-sized allocations") no longer differentiates the migration type of pages in THP-sized PCP list, it's possible that non-movable allocation requests may get a CMA page from the list, in some cases, it's not acceptable. If a large number of CMA memory are configured in system (for example, the CMA memory accounts for 50% of the system memory), starting a virtual machine with device passthrough will get stuck. During starting the virtual machine, it will call pin_user_pages_remote(..., FOLL_LONGTERM, ...) to pin memory. Normally if a page is present and in CMA area, pin_user_pages_remote() will migrate the page from CMA area to non-CMA area because of FOLL_LONGTERM flag. But if non-movable allocation requests return CMA memory, migrate_longterm_unpinnable_pages() will migrate a CMA page to another CMA page, which will fail to pass the check in check_and_migrate_movable_pages() and cause migration endless. Call trace: pin_user_pages_remote --__gup_longterm_locked // endless loops in this function ----_get_user_pages_locked ----check_and_migrate_movable_pages ------migrate_longterm_unpinnable_pages --------alloc_migration_target This problem will also have a negative impact on CMA itself. For example, when CMA is borrowed by THP, and we need to reclaim it through cma_alloc() or dma_alloc_coherent(), we must move those pages out to ensure CMA's users can retrieve that contigous memory. Currently, CMA's memory is occupied by non-movable pages, meaning we can't relocate them. As a result, cma_alloc() is more likely to fail. To fix the problem above, we add one PCP list for THP, which will not introduce a new cacheline for struct per_cpu_pages. THP will have 2 PCP lists, one PCP list is used by MOVABLE allocation, and the other PCP list is used by UNMOVABLE allocation. MOVABLE allocation contains GPF_MOVABLE, and UNMOVABLE allocation contains GFP_UNMOVABLE and GFP_RECLAIMABLE. Link: https://lkml.kernel.org/r/1718845190-4456-1-git-send-email-yangge1116@126.com Fixes: 5d0a661d808f ("mm/page_alloc: use only one PCP list for THP-sized allocations") Signed-off-by: yangge Cc: Baolin Wang Cc: Barry Song <21cnbao@gmail.com> Cc: Mel Gorman Cc: Signed-off-by: Andrew Morton --- mm/page_alloc.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) (limited to 'mm') diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 7300aa9f14b0..9ecf99190ea2 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -504,10 +504,15 @@ out: static inline unsigned int order_to_pindex(int migratetype, int order) { + bool __maybe_unused movable; + #ifdef CONFIG_TRANSPARENT_HUGEPAGE if (order > PAGE_ALLOC_COSTLY_ORDER) { VM_BUG_ON(order != HPAGE_PMD_ORDER); - return NR_LOWORDER_PCP_LISTS; + + movable = migratetype == MIGRATE_MOVABLE; + + return NR_LOWORDER_PCP_LISTS + movable; } #else VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER); @@ -521,7 +526,7 @@ static inline int pindex_to_order(unsigned int pindex) int order = pindex / MIGRATE_PCPTYPES; #ifdef CONFIG_TRANSPARENT_HUGEPAGE - if (pindex == NR_LOWORDER_PCP_LISTS) + if (pindex >= NR_LOWORDER_PCP_LISTS) order = HPAGE_PMD_ORDER; #else VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER); -- cgit v1.2.3-70-g09d2