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[2003:d8:2f20:da00:b70a:d502:3b51:1f2d]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3e7607cd9fasm5350431f8f.35.2025.09.12.00.18.06 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 12 Sep 2025 00:18:06 -0700 (PDT) Message-ID: <3a842ae3-f13a-4f5d-8870-d81cf1f0d56d@redhat.com> Date: Fri, 12 Sep 2025 09:18:05 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 4/4] mm: hugetlb: allocate frozen pages in alloc_gigantic_folio() To: Kefeng Wang , 20250910133958.301467-1-wangkefeng.wang@huawei.com, Andrew Morton , Oscar Salvador , Muchun Song , Zi Yan , Matthew Wilcox Cc: sidhartha.kumar@oracle.com, jane.chu@oracle.com, Vlastimil Babka , Brendan Jackman , Johannes Weiner , linux-mm@kvack.org References: <20250911065659.617954-1-wangkefeng.wang@huawei.com> <20250911065659.617954-5-wangkefeng.wang@huawei.com> <90e926c9-40cb-4791-8360-e3d145fe3503@redhat.com> <8508e8fb-77cc-43a7-8460-456f68a552ba@huawei.com> <667133bd-0021-4d4e-9cde-fc8c1324522a@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 6116240011 X-Stat-Signature: q49hwomj6giymcis9bik6ae7byb3h9tx X-Rspam-User: X-HE-Tag: 1757661491-563016 X-HE-Meta: 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 ARMrpBdC 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 12.09.25 08:57, Kefeng Wang wrote: > > > On 2025/9/12 2:56, David Hildenbrand wrote: >> On 11.09.25 11:11, Kefeng Wang wrote: >>> >>> >>> On 2025/9/11 16:25, David Hildenbrand wrote: >>>> On 11.09.25 08:56, Kefeng Wang wrote: >>>>> The alloc_gigantic_folio() allocates a folio by alloc_contig_range() >>>>> with refcount increated and then freeze it, convert to allocate a >>>>> frozen >>>>> folio directly to remove the atomic operation about folio refcount, >>>>> also >>>>> saving atomic operation during __update_and_free_hugetlb_folio too. >>>>> >>>>> Rename some functions to make them more self-explanatory, >>>>> >>>>>     folio_alloc_gigantic            -> folio_alloc_frozen_gigantic >>>>>     cma_{alloc,free}_folio          -> cma_{alloc,free}_frozen_folio >>>>>     hugetlb_cma_{alloc,free}_folio  -> hugetlb_cma_{alloc,free} >>>>> _frozen_folio >>>> >>>> Can we just get rid of folio_alloc_frozen_gigantic? >>>> >>> >>> OK, we could kill it. >>> >>>> Further, can we just get rid of cma_{alloc,free}_frozen_folio() as well >>>> and just let hugetlb use alloc_contig_range_frozen() etc? >>> >>> HugeTLB can allocate folio by alloc_contig_frozen_pages() directly, but >>> it could allocate from hugetlb_cma, cma_alloc_folio() need change some >>> cma metadata, so we need to keep it. >> >> Hm. Assuming we just have cma_alloc_frozen() -- again, probably what >> cma_alloc() would look like in the future, hugetlb can just construct a >> folio out of that. > > I get your point，firstly, we could convert to use cma_alloc_frozen() > instead of cma_alloc_folio() in hugetlb_cma_alloc_folio(). > >> >> Maybe we just want a helper to create a folio out of a given page range? >> >> And that page range is either obtained through cma_alloc_frozen() or >> alloc_contig_frozen_pages(). >> >> Just a thought, keeping in mind that these things should probably just >> work with frozen pages and let allcoating of a memdesc etc. be taken >> care of someone else. >> >> I'd be happy if we can remove the GFP_COMPOUND parameter from >> alloc_contig*. > > But not sure about this part, GFP_COMPOUND for alloc_contig* is > introduced by commit e98337d11bbd "mm/contig_alloc: support __GFP_COMP", > if we still allocate a range of order-0 pages and create a folio > outside, it will slow the large folio allocation. Assuming we leave the refcount untouched (frozen), I guess what's left is a) Calling post_alloc_hook() on each free buddy chunk we isolated b) Splitting all pages to order 0 Splitting is updating the page owner + alloc tag + memcg, and currently still updating the refcount. I would assume that most of the overhead came from the atomics when updating the refcount in split_page, which we would optimize out. Perf profile before: Alloc - 99.99% alloc_pool_huge_folio - __alloc_fresh_hugetlb_folio - 83.23% alloc_contig_pages_noprof - 47.46% alloc_contig_range_noprof - 20.96% isolate_freepages_range 16.10% split_page - 14.10% start_isolate_page_range - 12.02% undo_isolate_page_range Would be interesting trying to see how much overhead would remain when just dealing OTOH, maybe we can leave GFP_COMPOUND support in but make the function more generic, not limited to folios (I suspect many users will not want folios, except hugetlb). Maybe just a struct page * cma_alloc_compound(struct cma *cma, unsigned int order, unsigned int align, bool no_warn); That would allocate a frozen compoud page starting today already. -- Cheers David / dhildenb