From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 41A0BFCC9DE for ; Tue, 10 Mar 2026 08:44:04 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 9FE596B0088; Tue, 10 Mar 2026 04:44:03 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9B5DE6B0089; Tue, 10 Mar 2026 04:44:03 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8D4C46B008A; Tue, 10 Mar 2026 04:44:03 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 794486B0088 for ; Tue, 10 Mar 2026 04:44:03 -0400 (EDT) Received: from smtpin25.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 0A54B160527 for ; 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imf12.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf12.hostedemail.com: domain of dev.jain@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=dev.jain@arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1773132241; a=rsa-sha256; cv=none; b=Hu33te8xPA404qrr/8wR/AyqCjCn7mx93DeTpbPQx1ltIjZFi/f44qo/XV9tFR7abl/9r0 3lf20DudHDIdR43ClD+Pktl2kI1c+Kr0wkkQg8P2BSXylP964EU9K8bfQbhJQGDRhL2mnW yGO5TNernXgkvB0OtRYMpYIg75jNUcg= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id DC80D169C; Tue, 10 Mar 2026 01:43:53 -0700 (PDT) Received: from [10.164.19.59] (unknown [10.164.19.59]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 508BD3F7BD; Tue, 10 Mar 2026 01:43:51 -0700 (PDT) Message-ID: Date: Tue, 10 Mar 2026 14:13:48 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/9] mm/rmap: initialize nr_pages to 1 at loop start in try_to_unmap_one To: "Lorenzo Stoakes (Oracle)" 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 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> Content-Language: en-US From: Dev Jain In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 303EB40004 X-Stat-Signature: 5oy99uzq1553kiodu6u9p4q3nzitq789 X-Rspam-User: X-HE-Tag: 1773132240-795614 X-HE-Meta: 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 h1fua0lW 3v7d7c+DlE/SCw1/n65XLwkk+BhUb+LdCkOViAS+JWT4Izom279w+r3KdQseaP2Jr9DENafnrUk+m2UWDg8uTIhWU66RFy4lsVs3W6Ixl6FnGbtLOnMAVG9Tc9B6QuTvUprz9bF1YVOb3pLFPM0FpBazefha7OGJODdBpVmH8G1QQO8Zx8ORqff+Mo2YSJsyblpk0 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/03/26 2:09 pm, Lorenzo Stoakes (Oracle) wrote: > 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 :) Okay, thanks. > > Thanks, Lorenzo