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dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf02.hostedemail.com: domain of qi.zheng@linux.dev designates 91.218.175.89 as permitted sender) smtp.mailfrom=qi.zheng@linux.dev ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793697113; b=Jy8ZAIEWBlKoCjdQQl5KkTWySLUxu698hlOM9M3xtuyUf0TBVrTowHGiUbbS0G97RGO10q v9/wRyo33P2ZEEV6HU/1nXEuXdW5tjUaeyAU0IP3dBoF0XuBwV9wOmUK/CfkHnh/aS+MEn nIo91/rPDuafqlSnD2TfJZ6hZKNvkJc= X-Envelope-To: linux-mm@kvack.org DKIM-Signature: a=rsa-sha256; bh=4izyozmbuMGIzwBXwOGfCjpLSN/9aWgvEh8DalxY9c8=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793697108; v=1; x=1794301908; b=hWhGAMYnBWhe3NfVoxNafdUdTJ1qC/oGhHK7lSWu2kfOXs8GDMfIUqyVR+Zar7r+naniL2DB Y3XdksAVun3fVK6BXo5jmmq7slXW+o+6OuNAlthBKQlgPdr1v4kmMszOtXoaLlp1xSfQS0O/XAI Ph57qygITpzKfnDJXgJwcRrw= X-Envelope-To: linux-mm@kvack.org Received: by smtp.migadu.com with ESMTPS id 736b6edb0d423b19; Tue, 03 Nov 2026 09:11:48 +0000 X-Mizu-Trace-ID: 736b6edb0d423b19 X-Migadu-Flow: FLOW_OUT Message-ID: Date: Tue, 3 Nov 2026 17:11:39 +0800 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/4] mm: hugetlb: skip CMA when direct reclaim is disallowed To: sashiko-reviews@lists.linux.dev, muchun.song@linux.dev, osalvador@suse.de, david@kernel.org, akpm@linux-foundation.org, azpijr@gmail.com Cc: linux-mm@kvack.org, Qi Zheng References: <325d33655f29a2799a0859c788c48625feeb85f1.1793692578.git.zhengqi.arch@bytedance.com> From: Qi Zheng In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: C45E580006 X-Spam-Status: No, score=-12.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Stat-Signature: ah7qyhqz1tcoffauctty8sefwhu3s1yg X-HE-Tag: 1793697111-499014 X-HE-Meta: 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 5+0mL3pl 9ENRqKo8/vhviRgUN38Ivl7354pIpq6vWkv/qkE4/hNvcmoWn/jlYy0wEP6OUok5y1nrbVgYJQqMacqc6mB/tbjcxYCDhw6+1U6R6zKVS+BxioU+Ipm/uk8GHydiM0naK5ec4Du2WiGNMqC3Zzkbn0v55CHSm3981DKUtHCjJ29yD0kmCqle0QVCr7g7I2mHvb4ym6vprSXH0+fpARng18xYl75TrP+M2pkv0nCaae+j803F/I9Yhb/Csj3H/75UKdXxST0jhv7ezFEw7BMneEdaId5xVs3PqmXg+kzjo88IoSqY= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 11/3/26 4:47 PM, sashiko-bot@kernel.org wrote: > Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: > - [Medium] mm: hugetlb: hugetlb_cma_alloc_frozen_folio() breaks MPOL_PREFERRED_MANY > -- > > commit c96d52d66d643a77abaa96a17e392b7ab0f36ccd > Author: Qi Zheng > > mm: hugetlb: skip CMA when direct reclaim is disallowed > > This commit updates hugetlb_cma_alloc_frozen_folio() to return NULL when > gfpflags_allow_blocking(gfp_mask) is false, avoiding direct reclaim inside > cma_alloc_frozen_compound() when __GFP_DIRECT_RECLAIM was cleared by the > caller. > >> diff --git a/mm/hugetlb_cma.c b/mm/hugetlb_cma.c >> index dde1c866406fb..90f8d718a1f16 100644 >> --- a/mm/hugetlb_cma.c >> +++ b/mm/hugetlb_cma.c >> @@ -59,7 +59,7 @@ struct folio *hugetlb_cma_alloc_frozen_folio(int order, gfp_t gfp_mask, >> const nodemask_t *nmask; >> unsigned int cpuset_mems_cookie; >> >> - if (!hugetlb_cma_size) >> + if (!hugetlb_cma_size || !gfpflags_allow_blocking(gfp_mask)) >> return NULL; > > [Severity: Medium] > Does returning NULL from hugetlb_cma_alloc_frozen_folio() whenever > !gfpflags_allow_blocking(gfp_mask) break MPOL_PREFERRED_MANY for gigantic > surplus HugeTLB allocations? > > In mm/hugetlb.c, alloc_buddy_hugetlb_folio() implements MPOL_PREFERRED_MANY > as a two-pass allocation: > > mm/hugetlb.c:alloc_buddy_hugetlb_folio() { > if (mpoli->mode == MPOL_PREFERRED_MANY) { > gfp_t gfp = gfp_mask & ~(__GFP_DIRECT_RECLAIM | __GFP_NOFAIL); > > folio = alloc_surplus_hugetlb_folio(h, gfp, mpoli->nid, > nodemask); > > /* Fallback to all nodes if page==NULL */ > nodemask = NULL; > } > > if (!folio) { > folio = alloc_surplus_hugetlb_folio(h, gfp_mask, mpoli->nid, > nodemask); > } > } > > This reaches hugetlb_cma_alloc_frozen_folio() via: > > alloc_buddy_hugetlb_folio() > -> alloc_surplus_hugetlb_folio() > -> alloc_fresh_hugetlb_folio() > -> only_alloc_fresh_hugetlb_folio() > -> alloc_gigantic_frozen_folio() > -> hugetlb_cma_alloc_frozen_folio() > > On the first pass, __GFP_DIRECT_RECLAIM is cleared while nodemask points to > the preferred nodes (pol->nodes), and on the second pass nodemask is cleared > to NULL. Because hugetlb_cma_alloc_frozen_folio() now returns NULL on the > first pass, it never sees the MPOL_PREFERRED_MANY nodemask. > > In mm/hugetlb.c:alloc_gigantic_frozen_folio(): > > folio = hugetlb_cma_alloc_frozen_folio(order, gfp_mask, nid, nodemask); > if (folio) > return folio; > > if (hugetlb_cma_exclusive_alloc()) > return NULL; > > folio = (struct folio *)alloc_contig_frozen_pages(1 << order, gfp_mask, > nid, nodemask); > > When hugetlb_cma_exclusive_alloc() is false, returning NULL from > hugetlb_cma_alloc_frozen_folio() on the first pass falls through to > alloc_contig_frozen_pages() on the preferred nodes, bypassing the dedicated > hugetlb_cma pool on the preferred nodes in favor of non-CMA memory. > > When hugetlb_cma_exclusive_alloc() is true (or when non-CMA allocation fails > on the preferred nodes), the first pass returns NULL and the second pass > invokes hugetlb_cma_alloc_frozen_folio() with nodemask set to NULL. Since > mm/mempolicy.c:policy_nodemask() leaves *nid as numa_node_id() when > pol->home_node is NUMA_NO_NODE: > > mm/mempolicy.c:policy_nodemask() { > case MPOL_PREFERRED_MANY: > nodemask = &pol->nodes; > if (pol->home_node != NUMA_NO_NODE) > *nid = pol->home_node; > break; > } > > hugetlb_cma_alloc_frozen_folio() on the second pass tries > hugetlb_cma[numa_node_id()] and then iterates cpuset_current_mems_allowed > from node 0, allocating from non-preferred CMA nodes even when preferred > nodes in pol->nodes have free CMA pages. > > Prior to commit 9bda131c6093 ("mm: cma: add cma_alloc_frozen{_compound}()"), > cma_alloc_folio() forwarded gfp_mask down to alloc_contig_frozen_range(), > where __alloc_contig_verify_gfp_mask() preserved the cleared > __GFP_DIRECT_RECLAIM bit so CMA on the preferred nodemask was tried on the > first pass without entering direct reclaim. Would forwarding gfp_mask to Thanks for catching this. You're right: in CMA-only mode, this check skips the preferred-node attempt entirely. The fallback can then allocate from a non-preferred node even when the preferred nodes have usable CMA memory. > cma_alloc_frozen_compound() (in mm/cma.c) preserve both the non-reclaiming > first pass and the MPOL_PREFERRED_MANY nodemask? Make sense. I'll replace the check with GFP-mask propagation through cma_alloc_frozen_compound(). This restores the preferred-node CMA attempt while preserving the caller's __GFP_DIRECT_RECLAIM setting. Like the following: diff --git a/include/linux/cma.h b/include/linux/cma.h index 8555d38a97b1..caedd59bde03 100644 --- a/include/linux/cma.h +++ b/include/linux/cma.h @@ -53,7 +53,8 @@ extern bool cma_release(struct cma *cma, const struct page *pages, unsigned long struct page *cma_alloc_frozen(struct cma *cma, unsigned long count, unsigned int align, bool no_warn); -struct page *cma_alloc_frozen_compound(struct cma *cma, unsigned int order); +struct page *cma_alloc_frozen_compound(struct cma *cma, unsigned int order, + gfp_t gfp); bool cma_release_frozen(struct cma *cma, const struct page *pages, unsigned long count); diff --git a/mm/cma.c b/mm/cma.c index a10ea37a261d..c2605967d77a 100644 --- a/mm/cma.c +++ b/mm/cma.c @@ -929,9 +929,10 @@ struct page *cma_alloc_frozen(struct cma *cma, unsigned long count, return __cma_alloc_frozen(cma, count, align, gfp); } -struct page *cma_alloc_frozen_compound(struct cma *cma, unsigned int order) +struct page *cma_alloc_frozen_compound(struct cma *cma, unsigned int order, + gfp_t gfp) { - gfp_t gfp = GFP_KERNEL | __GFP_COMP | __GFP_NOWARN; + gfp |= __GFP_COMP | __GFP_NOWARN; return __cma_alloc_frozen(cma, 1 << order, order, gfp); } diff --git a/mm/hugetlb_cma.c b/mm/hugetlb_cma.c index 90f8d718a1f1..250b5c10d954 100644 --- a/mm/hugetlb_cma.c +++ b/mm/hugetlb_cma.c @@ -59,7 +59,7 @@ struct folio *hugetlb_cma_alloc_frozen_folio(int order, gfp_t gfp_mask, const nodemask_t *nmask; unsigned int cpuset_mems_cookie; - if (!hugetlb_cma_size || !gfpflags_allow_blocking(gfp_mask)) + if (!hugetlb_cma_size) return NULL; if (current->flags & PF_MEMALLOC_PIN) @@ -74,14 +74,16 @@ struct folio *hugetlb_cma_alloc_frozen_folio(int order, gfp_t gfp_mask, } if (hugetlb_cma[nid] && node_isset(nid, *nmask)) - page = cma_alloc_frozen_compound(hugetlb_cma[nid], order); + page = cma_alloc_frozen_compound(hugetlb_cma[nid], order, + gfp_mask); if (!page && !(gfp_mask & __GFP_THISNODE)) { for_each_node_mask(node, *nmask) { if (node == nid || !hugetlb_cma[node]) continue; - page = cma_alloc_frozen_compound(hugetlb_cma[node], order); + page = cma_alloc_frozen_compound(hugetlb_cma[node], order, + gfp_mask); if (page) break; } Thanks, Qi >