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Mon, 8 Dec 2025 05:40:41 -0500 (EST) Date: Mon, 8 Dec 2025 10:40:40 +0000 From: Kiryl Shutsemau To: Usama Arif Cc: Andrew Morton , Muchun Song , David Hildenbrand , Oscar Salvador , Mike Rapoport , Vlastimil Babka , Lorenzo Stoakes , Matthew Wilcox , Zi Yan , Baoquan He , Michal Hocko , Johannes Weiner , Jonathan Corbet , kernel-team@meta.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org Subject: Re: [PATCH 06/11] mm/hugetlb: Remove fake head pages Message-ID: References: <20251205194351.1646318-1-kas@kernel.org> <20251205194351.1646318-7-kas@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 9966D120015 X-Stat-Signature: yxh8qhisurdgt9nc9sp43q48bwo8a9tn X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1765190444-855928 X-HE-Meta: U2FsdGVkX1+ud7QEU4U0tZtUaI8RbJ7qxLYQlQZcBu0lipHuMT9kVNDLtKg/YTeFT9w/jatas+VlKd5cGleGbX47KYbMN0DbK5q1ESW837pDW3NC+4wqAchWy4bPCJPy8OQeOt2FxPOgjgT6JjZ1o8LLebuSLeqJH1sPXm7M5k0/khrAPcX4l+4E5CmDUMaCe3rm87dvLHGb3V3hVzDfPd5tCiitWdAF7iBqRO5+0kGD+kUGRR8BUU80lQUkgZpQnIn4iB7QeD6qBBCwPV3rZicZ3RZFtfBguriZOt7P8N2Cvncl4kpYZOHJfd4cYfqQ8C9UF6LVfk13qOIeNii8AY8AewfcB/QVXWwVINptOFBnSC9plY55yEteinEAL1RbydWmG8jYa6Fgz1+mhs8IkWOmcGBOpSCJT6AZrMTjS4ikk3ZeuVM/NITStU86Y70pPt0Xn5omI60/qSPe26PdkfLXUsNJL8qAp62Rt29FT9Cz63BVEGjyba8UgdFs+7pI60TToPSetMP6rrtZDhHWxFHL7Uf15mxvPIWWbl4q+03/7rpoTT9G+eBqUc/LhHTTrSerthJbN1VhseupwOhFTyCp1wJjDdGx9HrT91IaQaaA5E3wj71K86N9fFBS6m/vqWsCQZCW4bj8ZabHP9XBnHNzWk/420QiQ3hltQB4+SVkRM8gPIrjTYYGBsHSSGxsAOyhvuKKwVjvw4Kxg/SR8r79R+ClwyKcpWr/ijj7JgJUJvS/DFFlF6rzIenm3wFv34pF1gj11R+8mEI3ialreRQQxdzqDzSNwdl3/NV3kpNSU43Lce7theoEAxFWVSqK5cuvwt1Z/bOB95jKV/yX7ScuQ1E/a1KHBc8/KEoezjMWyNt8D8KxoEngOMjEBy/BYY6eRQcC0DgxZ9Th+nes7m1LirmpXuTpI0BPndQmtMPc1f1icKbFxVfqIouilVV7aq2tB8bM3895dnjfRrH AW0BnUQ/ p2XgvELBCb+/4UBrAzyaCM2nxsy6iNsw24YNehkgTncBD5QhJaSXieXoGiCsymgMChjbmBMlsHFe+nVIKBCf45FDptKKtLOlg5ZKt9l7WL9zrpFMBiZOzM8lfGM2UEvYUgP3Vj1XQCi8qMUdJSp2nxEXNQp79/U0880mNAy3Oza7DdgP25dsg1/a7KBeDiJu+ygzMv8eFChrHvlrPwCc9jSzYYCFKJHulywLykZY+l7fcmBj6knxxSQWYI9d1w6KctjF0xINQ7mHvHRFtPF2M10Rxlw== 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 Sat, Dec 06, 2025 at 05:03:25PM +0000, Usama Arif wrote: > > @@ -518,7 +519,24 @@ static bool vmemmap_should_optimize_folio(const struct hstate *h, struct folio * > > return true; > > } > > > > -static int __hugetlb_vmemmap_optimize_folio(const struct hstate *h, > > +static void hugetlb_vmemmap_tail_alloc(struct hstate *h) > > +{ > > + struct page *p; > > + > > + if (h->vmemmap_tail) > > + return; > > + > > The above check is unnecessary as we already check for > !h->vmemmap_tail in __hugetlb_vmemmap_optimize_folio? Right. I will streamline this codepath. > Is it possible that we could have a race here? Where 2 threads both > trying to allocate a hugetlb page when none exist in the system, both > see h->vmemmap_tail == NULL, both call alloc_page and set > h->vmemmap_tail? Good catch. Will fix. I guess, serializing h-vmemmap_tail with hugetlb_lock should be good enough. > Also, is there a good point where we can see that the number of > hstate->nr_huge_pages has gone down to 0 and free > h->vmemmap_tail? Its a single page per hstate so not a big deal, but > would be nice to have cleanup for it? I didn't want to go to this complexity, but if you folks think that it is needed, sure, can do. -- Kiryl Shutsemau / Kirill A. Shutemov