在 2024/12/13 16:23, Baolin Wang 写道:
On 2024/12/13 15:37, yangge1116@126.com wrote:
From: yangge yangge1116@126.com
Since commit 984fdba6a32e ("mm, compaction: use proper alloc_flags in __compaction_suitable()") allow compaction to proceed when free pages required for compaction reside in the CMA pageblocks, it's possible that __compaction_suitable() always returns true, and in some cases, it's not acceptable.
There are 4 NUMA nodes on my machine, and each NUMA node has 32GB of memory. I have configured 16GB of CMA memory on each NUMA node, and starting a 32GB virtual machine with device passthrough is extremely slow, taking almost an hour.
During the start-up of the virtual machine, it will call pin_user_pages_remote(..., FOLL_LONGTERM, ...) to allocate memory. Long term GUP cannot allocate memory from CMA area, so a maximum of 16 GB of no-CMA memory on a NUMA node can be used as virtual machine memory. Since there is 16G of free CMA memory on the NUMA node, watermark for order-0 always be met for compaction, so __compaction_suitable() always returns true, even if the node is unable to allocate non-CMA memory for the virtual machine.
For costly allocations, because __compaction_suitable() always returns true, __alloc_pages_slowpath() can't exit at the appropriate place, resulting in excessively long virtual machine startup times. Call trace: __alloc_pages_slowpath if (compact_result == COMPACT_SKIPPED || compact_result == COMPACT_DEFERRED) goto nopage; // should exit __alloc_pages_slowpath() from here
To sum up, during long term GUP flow, we should remove ALLOC_CMA both in __compaction_suitable() and __isolate_free_page().
Fixes: 984fdba6a32e ("mm, compaction: use proper alloc_flags in __compaction_suitable()") Cc: stable@vger.kernel.org Signed-off-by: yangge yangge1116@126.com
mm/compaction.c | 8 +++++--- mm/page_alloc.c | 4 +++- 2 files changed, 8 insertions(+), 4 deletions(-)
diff --git a/mm/compaction.c b/mm/compaction.c index 07bd227..044c2247 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -2384,6 +2384,7 @@ static bool __compaction_suitable(struct zone *zone, int order, unsigned long wmark_target) { unsigned long watermark; + bool pin; /* * Watermarks for order-0 must be met for compaction to be able to * isolate free pages for migration targets. This means that the @@ -2395,14 +2396,15 @@ static bool __compaction_suitable(struct zone *zone, int order, * even if compaction succeeds. * For costly orders, we require low watermark instead of min for * compaction to proceed to increase its chances. - * ALLOC_CMA is used, as pages in CMA pageblocks are considered - * suitable migration targets + * In addition to long term GUP flow, ALLOC_CMA is used, as pages in + * CMA pageblocks are considered suitable migration targets */ watermark = (order > PAGE_ALLOC_COSTLY_ORDER) ? low_wmark_pages(zone) : min_wmark_pages(zone); watermark += compact_gap(order); + pin = !!(current->flags & PF_MEMALLOC_PIN); return __zone_watermark_ok(zone, 0, watermark, highest_zoneidx, - ALLOC_CMA, wmark_target); + pin ? 0 : ALLOC_CMA, wmark_target); }
Seems a little hack for me. Using the 'cc->alloc_flags' passed from the caller to determin if ‘ALLOC_CMA’ is needed looks more reasonable to me.
Ok, thanks.
/* diff --git a/mm/page_alloc.c b/mm/page_alloc.c index dde19db..9a5dfda 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2813,6 +2813,7 @@ int __isolate_free_page(struct page *page, unsigned int order) { struct zone *zone = page_zone(page); int mt = get_pageblock_migratetype(page); + bool pin; if (!is_migrate_isolate(mt)) { unsigned long watermark; @@ -2823,7 +2824,8 @@ int __isolate_free_page(struct page *page, unsigned int order) * exists. */ watermark = zone->_watermark[WMARK_MIN] + (1UL << order); - if (!zone_watermark_ok(zone, 0, watermark, 0, ALLOC_CMA)) + pin = !!(current->flags & PF_MEMALLOC_PIN); + if (!zone_watermark_ok(zone, 0, watermark, 0, pin ? 0 : ALLOC_CMA)) return 0; }