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Mon, 16 Mar 2026 10:22:49 +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 Kq7pLvnZt2meVwAAD6G6ig (envelope-from ); Mon, 16 Mar 2026 10:22:49 +0000 Message-ID: <21f56de3-ec1a-4d7b-8abf-c538584e18b2@suse.de> Date: Mon, 16 Mar 2026 11:22:49 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 5/6] drm/gem-shmem: Track folio accessed/dirty status in mmap To: Boris Brezillon Cc: Biju Das , Tommaso Merciai , "loic.molinari@collabora.com" , "willy@infradead.org" , "frank.binns@imgtec.com" , "matt.coster@imgtec.com" , "maarten.lankhorst@linux.intel.com" , "mripard@kernel.org" , "airlied@gmail.com" , "simona@ffwll.ch" , "linux-mm@kvack.org" , "dri-devel@lists.freedesktop.org" References: <20260227114509.165572-1-tzimmermann@suse.de> <20260227114509.165572-6-tzimmermann@suse.de> <20260313111851.4c1f89f3@fedora> <20260313125644.65131b27@fedora> <20260313131835.52c5c935@fedora> <20260313134328.3166c4d0@fedora> <20260313135521.07823792@fedora> <20260313184549.08656eed@fedora> <53f11658-5466-49a3-816a-ff6fd2e1da6f@suse.de> <20260316103621.6ed48b68@fedora> Content-Language: en-US From: Thomas Zimmermann Autocrypt: addr=tzimmermann@suse.de; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Action: no action X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: D15721C0005 X-Stat-Signature: ambhk5djqowykb9zqsu1c3byybnewhqs X-Rspam-User: X-HE-Tag: 1773656572-814875 X-HE-Meta: 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 1m0Fp0HV Vt6IyPPd8QdnJniz7KyHaax1rkA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Am 16.03.26 um 10:36 schrieb Boris Brezillon: [...] >> This would keep the huge-page code within the first branch. And if it >> fails, it still does the regular page fault. > Well, in practice that's not what we want anyway (see the other fix for > the huge_fault vs regular fault race), so I'd still be inclined to have > the folio_mark_accessed() handled in the common path and have the pmd > vs regular pfn insertion in some if/else branches. Something like that: > > if (pmd_insert) > ret = drm_gem_shmem_try_insert_pfn_pmd(vmf, pfn); > else > ret = vmf_insert_pfn(vma, vmf->address, pfn); > > if (ret == VM_FAULT_NOPAGE) { > folio_mark_accesed(folio); > > /* Normal pages are mapped RO, and remapped RW afterwards. */ > if (pmd_insert && vmf->flags & FAULT_FLAG_WRITE) This style mixes conditions from different branching depths. The first outermost branch uses pmd_insert to compute ret.  Any then both have changed places, so that ret is in the outer branch and pmd_insert is in the inner branch.  This is hard to maintain. It is already confusing now and will be even more so to anyone locking at that code later on. Best regards Thomas > folio_mark_dirty(folio); > } -- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)