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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1u7O5z-00000006Uw5-0YtJ; Wed, 23 Apr 2025 00:36:11 +0000 Date: Wed, 23 Apr 2025 01:36:10 +0100 From: Matthew Wilcox To: Andrew Morton Cc: Shivank Garg , shaggy@kernel.org, david@redhat.com, wangkefeng.wang@huawei.com, jane.chu@oracle.com, ziy@nvidia.com, donettom@linux.ibm.com, apopple@nvidia.com, jfs-discussion@lists.sourceforge.net, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzbot+8bb6fd945af4e0ad9299@syzkaller.appspotmail.com Subject: Re: [PATCH V4 1/2] mm: add folio_migration_expected_refs() as inline function Message-ID: References: <20250422114000.15003-1-shivankg@amd.com> <20250422114000.15003-2-shivankg@amd.com> <20250422164111.f5d3f0756ad94d012180ece5@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250422164111.f5d3f0756ad94d012180ece5@linux-foundation.org> X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: B8F9C18000D X-Stat-Signature: 3utdtzycocr1hqx65bazf8enb7pc1eog X-Rspam-User: X-HE-Tag: 1745368587-999286 X-HE-Meta: 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 O4gxz1Gn tjBQdVUmYQmgHvyPMuNEf6Z4qoe8WtuGOq8quHfocq+FuBD/FDaxggQTSJBtkRmYQCqKc+EGUu2J9Z7O2mwi/tMk2Ezvx3QaCEKyo2x9PzfEPwIAsaMpwFs+MBV793c2E/FHX7c9ecmmbGx06div1CJNNysRtuPCkM1cs3eJV+We7oZuKNli2o/e2MxwyyP/OlMo9vwLr2oQBoDxfAqCa0pTaNmHjWdaFgd6PYvuj1qEd2wm3nzSZ+afyHyY2HSZN4FBxHQcZ0WEJwNxyJs6KPk759D/G8Pg0CdgwOc/7mGEq56hG9JXC4uF+MqWk4mqfKlIqOQqceBnzTlIQNIKl2Ut3FGDPFFtpNIEMy+7P8mL7cNWnEloQM0pLMA== 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, Apr 22, 2025 at 04:41:11PM -0700, Andrew Morton wrote: > > +/** > > + * folio_migrate_expected_refs - Count expected references for an unmapped folio. > > "folio_migration_expected_refs" Please run make W=1 fs/jfs/ in order to run kernel-doc on this file. It'll flag this kind of error. > It's concerning that one particular filesystem needs this - one > suspects that it is doing something wrong, or that the present API > offerings were misdesigned. It would be helpful if the changelogs were > to explain what is special about JFS. It doesn't surprise me at all. Almost no filesystem implements its own migrate_folio operation. Without going into too much detail, almost all filesystems can use filemap_migrate_folio(), buffer_migrate_folio() or buffer_migrate_folio_norefs(). So this is not an indication that jfs is doing anything wrong (except maybe it's misdesigned in that the per-folio metadata caches the address of the folio, but changing that seems very much too much work to ask someone to do). What I do wonder is whether we want to have such a specialised function existing. We have can_split_folio() in huge_memory.c which is somewhat more comprehensive and doesn't require the folio to be unmapped first. I currently lack the capacity to write pseudo-code illustrating what I mean, but I'll have a try tomorrow.