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Tue, 17 Jun 2025 12:50:40 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id J9wSF6BkUWj+SgAAD6G6ig (envelope-from ); Tue, 17 Jun 2025 12:50:40 +0000 Date: Tue, 17 Jun 2025 14:50:38 +0200 From: Oscar Salvador To: David Hildenbrand Cc: Andrew Morton , Muchun Song , James Houghton , Peter Xu , Gavin Guo , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/5] mm,hugetlb: Document the reason to lock the folio in the faulting path Message-ID: References: <1297fdd5-3de2-45bc-b146-e14061643fee@redhat.com> <11a1d0f7-ef4e-4836-9bde-d7651eebcd03@redhat.com> <3eb8e1e2-5887-47ed-addc-3be664dd7053@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Action: no action X-HE-Meta: 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 rceOiyqW TN/9DK+ghZx5IOlKueclckmkHfSm7k00vObUgQ37Ng6ZuGi/M9lVPPPltP7n9N/oPdn8M12aEIm1pMzcEBFrzJOksM/daRu4IG/ayUcTYoHzSIzg5tJreFWh4YqvsFODZhka4zNKe+6mrqsuhond7aFspI8wCulDVGklY6QFzcqNNq3YvXDi9c5LzsQ6cKHRu8JzDK13Rcnj1F72F8WjeeELhGUoY9pHWalLME/AyqGEZRSCfSxGQGLtb9CXscoSjnaul8fEMWL1ZCFQIlGUH6BKrbeUM++6rmwEx X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 43D3E180018 X-Stat-Signature: za616k87bpxnjnam1dgyrh5wu6x7prc1 X-Rspam-User: X-HE-Tag-Orig: 1750164642-872706 X-HE-Tag: 1750164645-331649 X-HE-Meta: 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 ac1CTMQT TvJOFo7eNlFMg9usEacJRzjt5GQPm+a1YuVEdLumsnrSrC35yNuFFNtwrBRIFRzB8to+lMc2RnaYFjjT5gkWbdxvpAWbubAj5ycW+NLazNJn7CLgDUPXzPKli6SRQdeO7cRVtgfz6BAW8PiO5lOz+vCHiRQRsj5ZkE+QfPTRX8PO204y0kjeZRWJCtzWzbwIkFVz3vB+Egu4GbFI= 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 Tue, Jun 17, 2025 at 02:10:09PM +0200, Oscar Salvador wrote: > On Tue, Jun 17, 2025 at 02:08:16PM +0200, David Hildenbrand wrote: > > folio lock is a sleeping lock, PTL is a spinlock. :) > > Lol yes, overlooked that totally. > And I also saw the comment from mm/rmap.c about lockin order. So, we could do something like this: if (folio_test_anon(old_folio)) { spin_unlock(vmf->ptl); folio_lock(old_folio); spin_lock(vmf->ptl); vmf->pte = hugetlb_walk(vma, vmf->address, huge_page_size(h)); if (unlikely(!vmf->pte || !pte_same(huge_ptep_get(mm, vmf->address, vmf->pte), pte))) { spin_unlock(vmf->ptl); folio_unlock(old_folio); goto out_take_lock; } if (folio_mapcount(old_folio == 1)) { if (!PageAnonExclusive(&old_folio->page)) { folio_move_anon_rmap(old_folio, vma); SetPageAnonExclusive(&old_folio->page); } if (likely(!unshare)) set_huge_ptep_maybe_writable(vma, vmf->address, vmf->pte); spin_unlock(vmf->ptl); folio_unlock(old_folio); goto out_take_lock; } VM_BUG_ON_PAGE(folio_test_anon(old_folio) && PageAnonExclusive(&old_folio->page), &old_folio->page); spin_unlock(vmf->ptl); folio_unlock(old_folio); spin_lock(vmf->ptl); vmf->pte = hugetlb_walk(vma, vmf->address, huge_page_size(h)); if (unlikely(!vmf->pte || !pte_same(huge_ptep_get(mm, vmf->address, vmf->pte), pte))) return 0; } Hopefully we can do some refactor here, because I quite dislike the unlock-lock-retake-unlock-blah cycle. -- Oscar Salvador SUSE Labs