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[2003:d8:2f20:da00:b70a:d502:3b51:1f2d]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3e7607770cesm5427830f8f.9.2025.09.12.00.23.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 12 Sep 2025 00:23:21 -0700 (PDT) Message-ID: <1da42002-9dad-45a7-98f8-90a97801002d@redhat.com> Date: Fri, 12 Sep 2025 09:23:19 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 4/4] mm: hugetlb: allocate frozen pages in alloc_gigantic_folio() From: David Hildenbrand 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> <3a842ae3-f13a-4f5d-8870-d81cf1f0d56d@redhat.com> Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 01E6C4000B X-Stat-Signature: 6mbi5s5ui8pkwtasbbu6c1z9cciqhbqc X-Rspam-User: X-HE-Tag: 1757661805-510917 X-HE-Meta: U2FsdGVkX1+N+fT2YffXgTqyp9mLgt0yz6WN5GkZdvx4QHAExWQX77pD5Se2abrAOEYk6ZV5NSkpGeGFyyc/KEK60w5d3DBAwY0lLTB11+pz28Rfu/qXtCyNTzwOEpWNYN9Eo0B/kZM2Gp+1COJDuVDYSAvFa7+E5ZIBO9Pk2S7rRQNQU5NKGATiHGpn3Qdu+z25xWeCoMFXgOKG8pWKegdsdBZyywlf/+zmcP3fD4L0096uGMU5BhruOxtUCt5Ypidv2BDVb0O/BD6Nz2WEnRJyGAaMNPdUY6tiOqem4XJr4+xX40EnFSVsJzlsdN9N3tQF0IEWTl8lMa5MUNXquHHOyfRIDmxL0ENTrws1u0+BxIHg5jHMaU2s00dUvsUq1nj0EMg6NXFuPvo8/uxP9+HceVOOBYbneaCpewcdlbIHbrMYnHpazYEiqkJBRRdC2c2D25OuXy/d/hezv7Il0oQeDdWR2pMpkwc4XyzFxMZdztWnOdthDNCftBVH7m9wxaxPJu8dn38/t7RST5WkAWiK+ovYMx+C9kkDK4nDvusayzN8de3q+u9mDLn8+0kG5wM27tlwPtiUfQuEr0oHAVNANewy/SLGuA343Bi+tmBCc9jxvsn77pjpnO2NBfTVFGfdmIk76IKByuxdG4em1Ls2k5ZhBIWzlnWHSANtHs82OCF0TugDUbuu8mYxNWeNmGA0f4EmfMsKKjZyPg1bSiTn8Ms3uL51YYUEv/F5ZObGDdJJeL7w6DlSFOfgWpqaBuO5tSh70XyeD+RFBtDJsfOxQNVHv0LYsHEHst09pWDQvTpRU6sqYCG7Mne94dMJVD3IGyb6PHjuelklp8oz93n9dh5eVrPJgOhu3V+Bmu3SfuIEup5hb2W+15ffCjbc7aVCQQOIR4Y3wVBo3wdnBImq4NCS7G/5v3xt2QweJmTqRap8DcKMmL1BVVKtFRToq7KVPfEyumuP38jZaYE 7kDKngs6 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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 09:18, David Hildenbrand wrote: > 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); ^ no need for the align as I realized, just like cma_alloc_folio() doesn't have. I do wonder why we decided to allow cma_alloc_folio() to consume gfp_t flags when we don't do the same for cma_alloc(). -- Cheers David / dhildenb