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b=PJVzTsn8qnM3BwB9BgTg/LvNeYXnPQsvVcU4MYqNHmq5qkQ/tReJgUdUVK8iKBhp3 BB2ZgNzWfwWT2Ah3uFVhvN4MXQw12bRYLVnmEdxiwds4bVH/Hkgmn9bmAMWsEHepNs 7hZ6ZCHYhd9ZhXd4V3CYlTk0QpLlEtLYNfw+EEiIgOIXTRFy/wXgoYyjyazHF0dvfy 3sh8QjuJ9obb5Cx5Hrb2neGzGKSQeVrEQfedVClEs848shDPB3jOXRceOQMlkOTg+U XIOq8EvqmpRZI5HQ4M6JrItRfJ9Hhp4LBw7rrZI26T/QBkueevkdYjHiEF56DBH/7R H6J0ZFZMvFFvw== Date: Mon, 17 Aug 2026 17:24:36 +0100 From: "Lorenzo Stoakes (ARM)" To: "David Hildenbrand (Arm)" Cc: Vernon Yang , akpm@linux-foundation.org, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, usama.arif@linux.dev, zokeefe@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Vernon Yang , stable@vger.kernel.org Subject: Re: [PATCH v2 1/3] mm: khugepaged: fix swap entry value to folio_pfn() Message-ID: References: <20260815051924.194810-1-vernon2gm@gmail.com> <20260815051924.194810-2-vernon2gm@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Stat-Signature: bwzay6uhdhpmfkkojk9983myy4c5obiy X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 2DFF818000F X-HE-Tag: 1786983896-836797 X-HE-Meta: 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 ox5/j9GJ Cj11WgVAyYq0Mcs7pKQPlDMZay/EfD4SilQuB5gyDAuhbVzUZsIv1lt+35IeqlP74mVobmAtwzOtddFBqvnTmNoqUkMxgKcrGvsNEyqzWZdwAxjrjr3GaFTk9Ssr9cFaSP0k3xIR8IGGQmIqlbMOuHBRCGGaxYEhV31BHSsiSwzBhW42da4VbUk8VWMpybyYg++n3Fb2NZNuivB3uYLC6ofi3S6App+fF/s+c0GHiVoMuWET1alV0cHkn1ud95U1mGpbpqFHoxxdoIVojRhYtZartiXB1nexgjtJfLcKpAC2t8qI= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Aug 17, 2026 at 06:19:16PM +0200, David Hildenbrand (Arm) wrote: > > > I mean maybe better to just reduce this to something like: > > > > /* folio is NULL unless exited early. */ > > trace_mm_khugepaged_scan_file(mm, > > (!folio || xa_is_value(folio)) ? -1 : folio_pfn(folio), > > file, present, swap, result); > > > > As the least invasive way of fixing the trace + limiting the contageon? > > I raised that using a folio after dropping relevant refs+locks is in general an > anti-pattern (IOW wrong if folios can just get split afterwards and are suddenly > no longer folios). > > I'd like us to avoid that where possible (and suspect Willy will thank us later ;) ) > > Isn't there some minimal way to just calculate the pfn once we obtain a folio? I > was assuming that there should be an easier way to do that. See my reply-to-self. My initial reply was wrong because parisc + mips do actually do classic sparsemem (sigh). I suggest what you're saying here basically. (Moving folio_put()'s for the break cases out of the loop is nasty) > > -- > Cheers, > > David -- Cheers, Lorenzo