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Tue, 20 Oct 2026 10:23:55 +0000 X-Mizu-Trace-ID: e512103824f9c4cb X-Migadu-Flow: FLOW_OUT Message-ID: <04c89538-28c8-4d03-92c1-08d854a46ac4@linux.dev> Date: Tue, 20 Oct 2026 18:23:49 +0800 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 5/5] mm: hugetlb: enable CMA allocation for PMD-sized pages To: Lance Yang Cc: muchun.song@linux.dev, osalvador@suse.de, david@kernel.org, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, zhengqi.arch@bytedance.com References: <20261020091653.14959-1-lance.yang@linux.dev> From: Qi Zheng In-Reply-To: <20261020091653.14959-1-lance.yang@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 37617C0008 X-Stat-Signature: gipigemi1a4r8h58y789ihtitss1f83o 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-Rspam-User: X-HE-Tag: 1792491836-573061 X-HE-Meta: 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 IMsqPPLV t6g0iIIZKLRDFAcfSjmtFQFHjnr7yc1AeTKUT2OlX0CfZ6SY+QJVV5p6oXW4tn2i1p3Ctjsg9vANeO6Nu0oocHBTbxYTRqJWvL6zxqQ9xpVC7Fbwgco1JffD9YXz6Zip4zUkXNtbf2ZnG/de9umN5NqVVdLDyxFkDrAfoVwwby4YCEc28c/rfhzKucAfDYaKYW6PLnjxA7JAIuMVW/3RdWIA825rrD4oL2cqN5XaTtIFFZQIgMYIT2Qxu2V0jkmJIRro7UtwWTaoBxiHvV+DpX6CKieBcnObvZHJlD0Knt+Ys0/I= 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 Hi Lance, On 10/20/26 5:16 PM, Lance Yang wrote: > > On Fri, Oct 16, 2026 at 06:07:36PM +0800, Qi Zheng wrote: >> From: Qi Zheng > [...] >> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >> index 218fbaee6f7e5..8c00fd9d0658d 100644 >> --- a/mm/hugetlb.c >> +++ b/mm/hugetlb.c >> @@ -1362,18 +1362,8 @@ static struct folio *dequeue_hugetlb_folio(struct hstate *h, gfp_t gfp_mask, >> static struct folio *alloc_gigantic_frozen_folio(int order, gfp_t gfp_mask, >> int nid, nodemask_t *nodemask) >> { >> - struct folio *folio; >> - >> - folio = hugetlb_cma_alloc_frozen_folio(order, gfp_mask, nid, nodemask); >> - if (folio) >> - return folio; >> - >> - if (hugetlb_cma_exclusive_alloc(order)) >> - return NULL; >> - >> - folio = (struct folio *)alloc_contig_frozen_pages(1 << order, gfp_mask, >> - nid, nodemask); >> - return folio; >> + return (struct folio *)alloc_contig_frozen_pages(1 << order, gfp_mask, >> + nid, nodemask); >> } >> #else /* !CONFIG_ARCH_HAS_GIGANTIC_PAGE || !CONFIG_CONTIG_ALLOC */ >> static struct folio *alloc_gigantic_frozen_folio(int order, gfp_t gfp_mask, int nid, >> @@ -1849,11 +1839,18 @@ static struct folio *only_alloc_fresh_hugetlb_folio(struct hstate *h, >> if (nid == NUMA_NO_NODE) >> nid = numa_mem_id(); >> >> - if (order_is_gigantic(order)) >> - folio = alloc_gigantic_frozen_folio(order, gfp_mask, nid, nmask); >> - else >> - folio = alloc_buddy_frozen_folio(order, gfp_mask, nid, nmask, >> - node_alloc_noretry); >> + folio = hugetlb_cma_alloc_frozen_folio(order, gfp_mask, nid, nmask); >> + if (!folio) { > > Emm ... what about PF_MEMALLOC_PIN here? > > If a FOLL_LONGTERM migration out of CMA needs a fresh hugetlb folio, > this can allocate another CMA folio as the target. > > With HVO disabled, the old folio is freed back to CMA and can be picked > again again again. > > I guess we'd keep migrating between CMA folios without ever completing > the pin ... even if pinnable buddy memory is available, no? Yes, you are right. A fresh migration target can come from CMA again, causing repeated migration without completing the pin, even when pinnable buddy memory is available. The same missing PF_MEMALLOC_PIN check also affects 1 GiB CMA allocations, so I had planned to fix it separately. Thanks, Qi > > [...] > > Cheers, Lance