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b=IgV+/w8O3GgzKq1ABNb2HtKj+DPFzHORrYG7fSDM5JH2L4g+/YjmwxspHj4bGvWye Wm+Wdd9OMD0rRKj+w3kWRJ7DcGkBZtcYVi2Ktc2uVsgpF9PcX+qikwgomItdNULvRV 3z+nI4yxFcfkqd4Z5HexyUGCuxH3V14QP99d5fOpWh2dZh8t45Q0ISXUx3rW/sPlOC 8xZwrKSqhlBHXweI2UYLq9iP4SS9vgTO0EzdZxs5IHdRMH30xnVgQEkWIqw++7VdR2 yuyOBV88edQ77ZwIs2PdOnKD9hGhsMwBSqqHCfgKzH+KgGaOV7j6OskXyknCanh3nK fB9S7PV8r/NrA== Date: Tue, 10 Mar 2026 08:39:27 +0000 From: "Lorenzo Stoakes (Oracle)" To: Dev Jain Cc: akpm@linux-foundation.org, axelrasmussen@google.com, yuanchu@google.com, david@kernel.org, hughd@google.com, chrisl@kernel.org, kasong@tencent.com, weixugc@google.com, Liam.Howlett@oracle.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, riel@surriel.com, harry.yoo@oracle.com, jannh@google.com, pfalcato@suse.de, baolin.wang@linux.alibaba.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, baohua@kernel.org, youngjun.park@lge.com, ziy@nvidia.com, kas@kernel.org, willy@infradead.org, yuzhao@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com Subject: Re: [PATCH 2/9] mm/rmap: initialize nr_pages to 1 at loop start in try_to_unmap_one Message-ID: References: <20260310073013.4069309-1-dev.jain@arm.com> <20260310073013.4069309-3-dev.jain@arm.com> <92b8f168-b135-4c2b-a0be-36c8f8079684@lucifer.local> <58b3878a-24fe-4ed1-a870-604b44da71f7@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <58b3878a-24fe-4ed1-a870-604b44da71f7@arm.com> X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 1191040006 X-Stat-Signature: 8sk4fxoi9kk1mpxnqdztsbci6huf5x1y X-Rspam-User: X-HE-Tag: 1773131978-317801 X-HE-Meta: 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 ruNw+bvY NYdubwVr6kDK+rjEf+M5yOci/Lhyu7zLbmt9pA7aCj+A3YThkRZ+iLdGIfDIRd5gaRF5Z3rObV25qkvUp/0GdXpi1g/yRGN5DE11AONOEunmMhF89Q1bzoSwiIm9WEfSIq2yTq27drsemQTRaOhCYcryKOUVVRfx3Jz6dvBj8HdBfFNC3tyCzqNiFW25GvC30BLbCjRwKlTarNd5oOSpAveE15ZUj+KZn4Y8+yap8uyLkwtBwBzyQUISW8OuAqGkC/QoGDPn6rkTeFuE= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Mar 10, 2026 at 02:01:44PM +0530, Dev Jain wrote: > > > On 10/03/26 1:40 pm, Lorenzo Stoakes (Oracle) wrote: > > On Tue, Mar 10, 2026 at 01:00:06PM +0530, Dev Jain wrote: > >> Initialize nr_pages to 1 at the start of the loop, similar to what is being > >> done in folio_referenced_one(). It may happen that the nr_pages computed > >> from a previous call to folio_unmap_pte_batch gets reused without again > >> going through folio_unmap_pte_batch, messing up things. Although, I don't > >> think there is any bug right now; a bug would have been there, if in the > >> same instance of a call to try_to_unmap_one, we end up in the > >> pte_present(pteval) branch, then in the else branch doing pte_clear() for > >> device-exclusive ptes. This means that a lazyfree folio has some present > >> entries and some device entries mapping it. Since a pte being > >> device-exclusive means that a GUP reference on the underlying folio is > >> held, the lazyfree unmapping path upon witnessing this will abort > >> try_to_unmap_one. > > > > Dude, paragraphs. PARAGRAPHS :) this is one dense set of words. > > > > It's also a very compressed 'stream of consciousness' hard-to-read block here. > > Sure :) I'll try to break this down. > > > > > I'm not sure it's really worth having this as a separate commit either, it's > > pretty trivial. > > Hmm...well, as I explain above, it's not trivial for me :) it is difficult > for me to reason here whether nr_pages can be reused without a reset in > a future iteration. OK you can have it be separate, let's just really clean up the commit message then please :) Thanks, Lorenzo