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b=a/tR3+7VlwCB16OuZnu7kef+T2i84B5dk13XMNTjd/UqdZmWmOnKUeFFdu44NqFDF TiQ225pHCcAUNz2U2kwDGry8PYe/v6YE3Aj/TBlilp92/KzDZ8HRa/NzKjKbrDEAXO qkS+YRR6O9YFmvfvEzDbQL8au8Bim0G8IG1fqtAs= Date: Thu, 26 Jun 2025 14:39:29 -0700 From: Andrew Morton To: Luiz Capitulino Cc: david@redhat.com, willy@infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lcapitulino@gmail.com, shivankg@amd.com Subject: Re: [PATCH 1/3] mm: introduce snapshot_page() Message-Id: <20250626143929.a7f2bcbb8e90290f23af452e@linux-foundation.org> In-Reply-To: <4a9745dd2989f7d5bf5bc69c37fc3e3cfda37e87.1750961812.git.luizcap@redhat.com> References: <4a9745dd2989f7d5bf5bc69c37fc3e3cfda37e87.1750961812.git.luizcap@redhat.com> X-Mailer: Sylpheed 3.7.0 (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-Rspamd-Queue-Id: 3C1074000D X-Stat-Signature: nxst4gyqxfcujhajiuwkzstkiu4gkfei X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1750973972-640339 X-HE-Meta: U2FsdGVkX1/+Vf8VXEBAmX9wSVwFeYy/rYQGSj/3QSJPXMgDkaF0xM0hcyyzAH52jgigu2qX76UmnuuiCTR4tqIxe7eZOHl3WFOGPRvYyPC8wksaEibvdA3uPL/lvSPu7sHlxfacyLcnG/htlBCt68zKOGZEsUbkF5BhDzPV0UkUSJEcvzo9AWAoKQ9nj1HhxBJhvxcckb1EGwKEVwt3LBB/v3bVcbuvIwS582e8inQuO0XKAeCaoTsCzxpIakUk2epBRnGV2wXva6KgYdSZ7zlqELD+rd8VvJg6CAPlh0y+mNHKUiZziUOBTusEvLh+rtdEUyfDXMQs3OG+ql+7j0ylF5t3xaTC9Ff5LL1oGlgygBfKPdpwaV8piih3c+W66iDQ/Imx1GYil9uljDKD+NqSv0RVfr3rt3EGIpmbYonDHGo05uUpSSZLqkPxOliuOcuiQ+E5zvgWkzH3tw31ak1jFmp7RjffniloZQPSk1WuYiZ1J8cQOUeijBSZ/LDLTJyHKsvnSD5+9NpvJQr/kHyunuw9W6rQ/RI6FcH8/bkOOuvwh0LSI1+V0xzVi/53w+HMqFLPzzTDTHl07/EnBwejkiTrIk+rVb6Qegh2XiAWle7OUk93THqM/yVZuF4ext5CdQYXQWdDgMhC8HZJy1vsWanuQiS6Bp02ipbjmzjiOKZkuvU/8ksPTXqwgSV0uGrbq+q/ChwTPGddaBuf2E7OaxuDaOPqAYPyThqx6AHcHNehho8LKZQunqLVS+ztsE82Z4IZlGCqWG6GxkJAQWjdkXwLnJlmCkUxOdCBSdaAdms4UHFdrmOty3bvX5xNRchP4lZHkJh0teOsrT3XqusOQvzpbken3J+kxEKOjUblKFKL81vnz59ee6bWQGkPSk4W2i67MrhtwlR8kfOcV2cN7t+bI4AK3u6hzfCnGddSMrBCR7vRrrnpwQCI8ij+zI6DYvF0hc8ZPFKM10+ LW9DN0U+ +/lv5Zb3tsOP0lrKeQ8OVyS3Vjv9y7Q1EpZke255QrDXzQBihFO4mULgbcylln1MzSrVq6Rv/cvv3UnWmUpsmBatVB9lCeU4ihhNzY+ZAhTl3AuRPMUnCrATNdLWjyI03VIm1j2pW4fG6sv1KognxvGbYYe7IlW2guAgonVfft7OIe3oX0gLkSIPFLxmVZxuPE1VVG7WWXvRwp6ZkFa/QIOexWjZGni5YHaMr4UwRyOLbXTtc0p+f8t4wLfhdnJH3DgsDM+t5bUatD/PYCvGfW+ZC3X4DwqXB7E3TKtYSPUs4CaOp2eK3MqTaui+xVgrN0I8SWNAtsIkhFmK78N6q1IX4WoJaI5K1lqDd 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 Thu, 26 Jun 2025 14:16:51 -0400 Luiz Capitulino wrote: > This commit refactors __dump_page() into snapshot_page(). > > snapshot_page() tries to take a faithful snapshot of a page and its > folio representation. The snapshot is returned in the struct > page_snapshot parameter along with additional flags that are best > retrieved at snapshot creation time to reduce race windows. > > This function is intended to be used by callers that need a stable > representation of a struct page and struct folio so that pointers > or page information doesn't change while working on a page. > > The idea and original implemenetation of snapshot_page() comes from tpyo! > Matthew Wilcox with suggestions for improvements from David Hildenbrand. > All bugs and misconceptions are mine. > > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -4184,4 +4184,24 @@ static inline bool page_pool_page_is_pp(struct page *page) > } > #endif > > +#define PAGE_SNAPSHOT_FAITHFUL (1 << 0) > +#define PAGE_SNAPSHOT_PG_HUGE_ZERO (1 << 1) > +#define PAGE_SNAPSHOT_PG_FREE (1 << 2) > +#define PAGE_SNAPSHOT_PG_IDLE (1 << 3) > + > +struct page_snapshot { > + struct folio folio_snapshot; > + struct page page_snapshot; > + unsigned long pfn; > + unsigned long idx; > + unsigned long flags; > +}; > + > +static inline bool snapshot_page_is_faithful(const struct page_snapshot *ps) > +{ > + return ps->flags & 0x1;' & PAGE_SNAPSHOT_FAITHFUL? > +} > + All looks sane to me. Small-system people (are there any left?) might point out that all the new code could be under ifdef CONFIG_PROCFS? I'll skip v1, see what reviewers have to say, thanks.