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b=hN44Nm1DtA0TsRaNPP0YSvHoRMNhpn0mknicuCZXaA1cMwoM4vpY8ko9mS8kKy3d2 vV8oRDc78Xzgep0qd/jYv9FHehacIwFeZ4S3Q513J5h8oYGR42ocIYDJKCM/JCYlHH lkiDhWT6wB8bZee2QxBTiAw0yCkkRDK806QYVSL8= Date: Mon, 22 Dec 2025 10:14:19 -0800 From: Andrew Morton To: Wei Yang Cc: david@kernel.org, lorenzo.stoakes@oracle.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, linux-mm@kvack.org Subject: Re: [Patch v3] mm/huge_memory: simplify page tracking in remap_page() during folio split Message-Id: <20251222101419.10e73a9f2b35df440abd8a62@linux-foundation.org> In-Reply-To: <20251222134531.20968-1-richard.weiyang@gmail.com> References: <20251222134531.20968-1-richard.weiyang@gmail.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 457EBC000B X-Stat-Signature: paruh9rkgjucj34eeszxnfi3yxuf17yb X-HE-Tag: 1766427261-578783 X-HE-Meta: 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 JG5C6O8n VFejfDf1j1XqZCC2zIzSsFEdd+9JRn9aqyLSMymN8JV0vWpwNDIBuqjCcSpxOIEhnmTuo42IXGj6pC3+H0uYg8BztC+E2D5FH4hyuPgVt0Vu2Fe/VErEB7zxP3YKp1zty7+pSv8zDEX7cSK6+2MQ+8itZLzhF+hMFCp5BAa/j7InhgGLfHBLAtp1afvtbuYE3N/H1fpeFjQXcfru+U0wfbtTL/UpJ6kTZyGdU70ojHjq93M4qy0Oh+zA7Ew4zM0YfrOK5NOf0nl61G531jBSvqOIAahqjYiyCX/cdLjt/n7zfBCH1/QKEVEgWr/XZNz+chPwyIqxzfSHeQ/XEtQOOtytyEjCjfcxilEvIsN5CfwZzKUDeKuEe/R4CoqVy+Kyi2RzksDYJAPN8rxc= 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 Mon, 22 Dec 2025 13:45:31 +0000 Wei Yang wrote: > After splitting a large folio, the resulting anonymous folios must be > remapped. > > Currently, the code tracks progress by recording the number of processed > pages in an index variable (e.g., @i) and comparing it against the > total. This commit simplifies the logic by directly subtracting the > processed pages from the remaining count. This approach is more > straightforward and reduces the number of local variables. > > Additionally, this commit renames the variable nr to nr_pages to improve > code readability and self-documentation. > > ... > > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -3423,17 +3423,15 @@ bool unmap_huge_pmd_locked(struct vm_area_struct *vma, unsigned long addr, > return __discard_anon_folio_pmd_locked(vma, addr, pmdp, folio); > } > > -static void remap_page(struct folio *folio, unsigned long nr, int flags) > +static void remap_page(struct folio *folio, unsigned long nr_pages, int flags) > { > - int i = 0; > - > /* If unmap_folio() uses try_to_migrate() on file, remove this check */ > if (!folio_test_anon(folio)) > return; > for (;;) { > remove_migration_ptes(folio, folio, RMP_LOCKED | flags); > - i += folio_nr_pages(folio); > - if (i >= nr) > + nr_pages -= folio_nr_pages(folio); > + if (!nr_pages) > break; > folio = folio_next(folio); > } This changes behavior when nr_pages was too large. It would be best to mention this and to describe why this is OK. Or to check for ((signed)nr_pages <= 0). Also, isn't it a bit nasty to alter an incoming arg? I think it's best to treat all those as const - part of the function's calling environment. Yes, C permits this hack but that was a mistake!