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Tue, 14 Jan 2025 12:01:06 -0800 (PST) MIME-Version: 1.0 References: <791d4056-cac1-4477-a8e3-3a2392ed34db@redhat.com> <1fdc9d50-584c-45f4-9acd-3041d0b4b804@redhat.com> <54ebdef4205781d3351e4a38e5551046482dbba0.camel@kernel.org> <2848b566-3cae-4e89-916c-241508054402@redhat.com> <060f4540-6790-4fe2-a4a5-f65693058ebf@fastmail.fm> In-Reply-To: From: Miklos Szeredi Date: Tue, 14 Jan 2025 21:00:55 +0100 X-Gm-Features: AbW1kvZIbaY8yr45F5FQPamVY8i3T8PpfIf_rUSauH1zAJbBRwND1-UeHpCqnEQ Message-ID: Subject: Re: [PATCH v6 4/5] mm/migrate: skip migrating folios under writeback with AS_WRITEBACK_INDETERMINATE mappings To: Joanne Koong Cc: Bernd Schubert , Jeff Layton , David Hildenbrand , Shakeel Butt , Zi Yan , linux-fsdevel@vger.kernel.org, jefflexu@linux.alibaba.com, josef@toxicpanda.com, linux-mm@kvack.org, kernel-team@meta.com, Matthew Wilcox , Oscar Salvador , Michal Hocko Content-Type: text/plain; charset="UTF-8" X-Stat-Signature: a3emjxt9m4geu4jfug9xtw5c9h8swn3c X-Rspam-User: X-Rspamd-Queue-Id: D77DE100019 X-Rspamd-Server: rspam08 X-HE-Tag: 1736884867-522435 X-HE-Meta: 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 9AM3UIv/ k2CcM4mewJsHo+X2G+8oyOwtRc3UEh9a1IGmz4Km7v6CNHfSw+UgjvE/gF8OZpyKkBArq5QveGfggbrD8gf5W6MdnmUI3+RAmACJ95m9OqHoZezs3yj+QatXNgJuvowUerzzbpYj0Xbdkw6ybbbCJcF1x8rJPehcWIGrt+HUWoGOaklN7dmbwYqwwNlkI/rk6hBCWGS1xpeTwb6RcUT337vBudkDrR5bGWDcn38N+zwHWYi3tsvvuNkdxMHqBwUSsKz6aohJEePz8W+c= X-Bogosity: Ham, tests=bogofilter, spamicity=0.016855, 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, 14 Jan 2025 at 20:12, Joanne Koong wrote: > If we copy the cache page, do we not have the same issue with needing > an rb tree to track writeback state since writeback on the original > folio would be immediately cleared? Writeback would not be cleared in that case. The copy would be to guarantee that the page can be migrated. Starting migration for an under-writeback page would need some new mechanism, because currently that's not possible. But I realize now that even though write-through does not involve PG_writeback, doing splice will result in those cache pages being referenced for an indefinite amount of time, which can deny migration. Ugh. Same as page reading, this exists today. Thanks, Miklos