From ee040cbd6e48165ba543c1d0405596283b1514ca Mon Sep 17 00:00:00 2001 From: Baokun Li Date: Wed, 5 Nov 2025 16:56:52 +0800 Subject: [PATCH] mm/page_alloc: don't warn about large allocations with __GFP_NOFAIL Filesystems use __GFP_NOFAIL to allocate block-sized folios for metadata reads at critical points, since they cannot afford to go read-only, shut down, or enter an inconsistent state due to memory pressure. Currently, attempting to allocate page units greater than order-1 with the __GFP_NOFAIL flag triggers a WARN_ON() in __alloc_pages_slowpath(). However, filesystems supporting large block sizes (blocksize > PAGE_SIZE) can easily require allocations larger than order-1. As Matthew Wilcox noted in [1], if we have a filesystem with 64KiB sectors, there will be many clean folios in the page cache that are 64KiB or larger. He also explained in [2] why kvmalloc isn't a valid approach here. With gfp flags and order already included in the OOM report, both Vlastimil Babka and Michal Hocko suggested that we can take the risk of removing this warning first and then observe whether a large number of related OOM reports appear. If that happens, we can consider adding special handling in other places. Link: https://lkml.kernel.org/r/20251105085652.4081123-1-libaokun@huaweicloud.com Signed-off-by: Baokun Li Suggested-by: Matthew Wilcox Link: https://lore.kernel.org/all/aQPX1-XWQjKaMTZB@casper.infradead.org [1] Link: https://lore.kernel.org/all/aQTHMI3t5mNXp0M1@casper.infradead.org [2] Suggested-by: Vlastimil Babka Link: https://lore.kernel.org/all/188a95ba-6384-4319-bb74-c0d9ec6c4079@suse.cz Suggested-by: Michal Hocko Link: https://lore.kernel.org/all/aQotQBjnDDeL_wHx@tiehlicka Acked-by: Michal Hocko Acked-by: Vlastimil Babka Cc: Brendan Jackman Cc: ErKun Yang Cc: Jan Kara Cc: Johannes Weiner Cc: Shakeel Butt Cc: Suren Baghdasaryan Cc: "zhangyi (F)" Cc: Zi Yan Signed-off-by: Andrew Morton --- mm/page_alloc.c | 5 ----- 1 file changed, 5 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index fb91c566327c1..e4efda1158b25 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -4683,11 +4683,6 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, int reserve_flags; if (unlikely(nofail)) { - /* - * We most definitely don't want callers attempting to - * allocate greater than order-1 page units with __GFP_NOFAIL. - */ - WARN_ON_ONCE(order > 1); /* * Also we don't support __GFP_NOFAIL without __GFP_DIRECT_RECLAIM, * otherwise, we may result in lockup. -- 2.47.3