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npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, linux-mm@kvack.org, wang lian Subject: Re: [Patch v3 4/4] mm/huge_memory: optimize old_order derivation during folio splitting Date: Thu, 30 Oct 2025 21:55:18 -0400 X-Mailer: MailMate (2.0r6272) Message-ID: In-Reply-To: <20251031015053.n44qkbtnmwbtpfmv@master> References: <20251021212142.25766-1-richard.weiyang@gmail.com> <20251021212142.25766-5-richard.weiyang@gmail.com> <9A89CDDB-7C17-4804-8240-E068EA68F7D2@nvidia.com> <20251031015053.n44qkbtnmwbtpfmv@master> Content-Type: text/plain Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: MN2PR06CA0024.namprd06.prod.outlook.com (2603:10b6:208:23d::29) To DS7PR12MB9473.namprd12.prod.outlook.com (2603:10b6:8:252::5) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS7PR12MB9473:EE_|SA1PR12MB7224:EE_ X-MS-Office365-Filtering-Correlation-Id: d0dfe46e-bed1-4c3b-0dd1-08de18208bd8 X-MS-Exchange-SenderADCheck: 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 atURtTyO ZcP0Q8HEC6VHA8WWbGqh6jIvIt4KD1ZBAxrIJ3QKXMU48o4+NA0d2hszSGaLbVI8DudVK+lDhweZtW1vkglOm88ckbzR/vQEkleBHsRYh7rlvDC/3X2J2Xx8mN6aBZj33p7iC41VbHUwWBq7/qoemK/NeOxgYBe+kGXfEGIbjvJa9m17JDwTMuv+DrAv0kuYHrC0q7BcEZoy1y3Iaz061pJgZGapa2r/ZRDcvLR8jwQpJ1bOt5VGad9w3xj/Rm6RMRXHBKsVi8YFN95Wo0N02YUTokYvfPxOgDqgpAEWgPj0eVYyoVxxEsJG5gN9nZ2axgPlyn/Tfct7HFSIpKcU7EsBKOM1F+QtD2vqRS05SaGaHJkAoq+f2KxKQ87ABWDEtYyxudtEa4YeeKCuXSkL+KYBRrWAZnhwzkoTiXcaBuGIQT7Oz6uved9AkQrwkfKISas+8 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 30 Oct 2025, at 21:50, Wei Yang wrote: > On Fri, Oct 24, 2025 at 11:29:00AM -0400, Zi Yan wrote: >> On 24 Oct 2025, at 10:46, Lorenzo Stoakes wrote: > [...] >>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>>> index 093b3ffb180f..a4fa8b0e5b5a 100644 >>>> --- a/mm/huge_memory.c >>>> +++ b/mm/huge_memory.c >>>> @@ -3596,8 +3596,8 @@ static int __split_unmapped_folio(struct folio= *folio, int new_order, >>>> struct address_space *mapping, bool uniform_split) >>>> { >>>> const bool is_anon =3D folio_test_anon(folio); >>>> - int order =3D folio_order(folio); >>>> - int start_order =3D uniform_split ? new_order : order - 1; >>>> + int old_order =3D folio_order(folio); >>>> + int start_order =3D uniform_split ? new_order : old_order - 1; >>>> int split_order; >>>> >>>> folio_clear_has_hwpoisoned(folio); >>>> @@ -3609,14 +3609,11 @@ static int __split_unmapped_folio(struct fol= io *folio, int new_order, >>>> for (split_order =3D start_order; >>>> split_order >=3D new_order; >>> >>> A thought for the future - now things are simplified, it might be nic= e to just >>> separate out the core of this loop and have the uniform split just ca= ll the >>> split out function directly, and the non-uniform one do the loop. >>> >>> As it's a bit gross in the uniform case we just let split_order go to= new_order >>> - 1 to exit the loop. >> >> Yeah, something like: >> >> if (uniform_split) { >> if (mapping) >> xas_split(xas, folio, old_order); >> split_folio_to_order(...); >> return 0; >> } >> >> for () { >> ... >> split_folio_to_order(...); >> ... >> } >> >> where split_folio_to_order(...) just >> split memcg, split page owner, pgalloc_tag_split, __split_folio_to_ord= er, >> and stats update >> > > This looks reasonable, while I found we already have split_folio_to_ord= er(). Then, we just need a new name, like __split_folio_and_update_stats(). I am bad at naming. Feel free to come up with a better one. :) > >>> >>> BUT - let's please save that for another patch :) >> >> I agree. >>> >>> This all looks fine. >>> >>>> split_order--) { >>>> - int old_order =3D folio_order(folio); >>>> int nr_new_folios =3D 1UL << (old_order - split_order); >>>> >>>> /* order-1 anonymous folio is not supported */ >>>> if (is_anon && split_order =3D=3D 1) >>>> continue; >>>> - if (uniform_split && split_order !=3D new_order) >>>> - continue; >>>> >>>> if (mapping) { >>>> /* >>>> @@ -3643,7 +3640,13 @@ static int __split_unmapped_folio(struct foli= o *folio, int new_order, >>>> mod_mthp_stat(old_order, MTHP_STAT_NR_ANON, -1); >>>> mod_mthp_stat(split_order, MTHP_STAT_NR_ANON, nr_new_folios); >>>> } >>>> + /* >>>> + * If uniform split, the process is complete. >>>> + * If non-uniform, continue splitting the folio at @split_at >>>> + * as long as the next @split_order is >=3D @new_order. >>>> + */ >>>> folio =3D page_folio(split_at); >>>> + old_order =3D split_order; >>>> } >>>> >>>> return 0; >>>> -- >>>> 2.34.1 >>>> >>>> >> >> >> -- >> Best Regards, >> Yan, Zi > > -- = > Wei Yang > Help you, Help me -- Best Regards, Yan, Zi