On Thu, Jun 20, 2024 at 12:55 AM yangge1116@126.com wrote:
From: yangge yangge1116@126.com
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.
Fixes: 5d0a661d808f ("mm/page_alloc: use only one PCP list for THP-sized allocations")
Please add the below tag
And I don't think 'mm/page_alloc: add one PCP list for THP' is a good title. Maybe:
'mm/page_alloc: Separate THP PCP into movable and non-movable categories'
Whenever you send a new version, please add things like 'PATCH V2', 'PATCH V3'. You have already missed several version numbers, so we may have to start from V2 though V2 is wrong.
Signed-off-by: yangge yangge1116@126.com
include/linux/mmzone.h | 9 ++++----- mm/page_alloc.c | 9 +++++++-- 2 files changed, 11 insertions(+), 7 deletions(-)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index b7546dd..cb7f265 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -656,13 +656,12 @@ enum zone_watermarks { };
/*
- One per migratetype for each PAGE_ALLOC_COSTLY_ORDER. One additional list
- for THP which will usually be GFP_MOVABLE. Even if it is another type,
- it should not contribute to serious fragmentation causing THP allocation
- failures.
- One per migratetype for each PAGE_ALLOC_COSTLY_ORDER. Two additional lists
- are added for THP. One PCP list is used by GPF_MOVABLE, and the other PCP list
*/
- is used by GFP_UNMOVABLE and GFP_RECLAIMABLE.
#ifdef CONFIG_TRANSPARENT_HUGEPAGE -#define NR_PCP_THP 1 +#define NR_PCP_THP 2 #else #define NR_PCP_THP 0 #endif diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 8f416a0..0a837e6 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -504,10 +504,15 @@ static void bad_page(struct page *page, const char *reason)
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); -- 2.7.4