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smtp.kernel.org (Postfix) with ESMTPSA id D0E3FC4CEDD; Tue, 14 Jan 2025 20:29:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1736886595; bh=P9Akyyhraz3cBw9JIfmKAtLEjUC7OhizULj/3rsA7WE=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=Pgf9ZszyV9fm/ASnPBJV3D4PsOCecZeKwgX9UqkyxGhgOXdLN7RHf5GMF9RLpd/CP Y424t76+R0bP3VshLL/5TjrH5oSGGtfnpyV+DGM7ag/132XBvV3zGPk0JbcaL/kvAG 4OJTpPG8FGzEN8lyfkjyIOAw1DtYfNKjF1h2h2HZhHyxpEkj+9tTVhJqaLSphtOsMw y9Bgv8+6lF8hg5YZxkNVoejjKiGRzCAzksOlaM0lkK+Jpmq6uHHR5LmblTCi7io2Xs bZNbnrZV3pL6YfqH1tC6efnHnsvqKGp8GSnTZDoBkC1NPfHfwn1Y69wGIUlDSOSy/F PFLcRi4gTl9pw== Message-ID: Subject: Re: [PATCH v6 4/5] mm/migrate: skip migrating folios under writeback with AS_WRITEBACK_INDETERMINATE mappings From: Jeff Layton To: Joanne Koong , Miklos Szeredi Cc: Bernd Schubert , 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 Date: Tue, 14 Jan 2025 15:29:52 -0500 In-Reply-To: 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> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV YrOOI5VGLHge0awt7bhMCTM9KAfPc+xL/ZxAMVWd3NCk5SamL2cE99UWgtvNOIYU8m6EjTLhsj8sn VluJH0/RcxEeFbnSaswVChNSGa7mXJrTR22lRL6ZPjdMgS2Km90haWPRc8Wolcz07Y2se0xpGVLEQ 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 8Au/Nv4T 0epMZjY3l6dXtsPhz0jti0ko1Ocg4Fc8Lyy8AEDP+1Jp3Qm3J3oEVlBhbIsQufTsKjV2TL2UUkhiP2LvWRwKTbQQe/ABD7/0H7isnu4L7CUoCmQD/hMBb3g9OKsEpHOrzgJBn72uDuCTT/80OWnM052tN8eFjhL129lViTsArHDKCzjw/TlEnMison44mFJ7agSF/kvI/gUB852f2sFXYTh+kZI7INSvkQmsSkuW4TyVcK1D1eSiL8naBlCWl5eid9wXHPLxIKYbVXB+hjfftXX9ISy+eVe9wGZm3dSr3ZzmfkDGg3D0mgFBDmkK6P9d9O9YX 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, 2025-01-14 at 11:12 -0800, Joanne Koong wrote: > On Tue, Jan 14, 2025 at 10:58=E2=80=AFAM Miklos Szeredi wrote: > >=20 > > On Tue, 14 Jan 2025 at 19:08, Joanne Koong wro= te: > >=20 > > > - my understanding is that the majority of use cases do use splice (e= g > > > iirc, libfuse does as well), in which case there's no point to this > > > patchset then > >=20 > > If it turns out that non-splice writes are more performant, then > > libfuse can be fixed to use non-splice by default. It's not as clear > > cut though, since write through (which is also the default in libfuse, > > AFAIK) should not be affected by all this, since that never used tmp > > pages. >=20 > My thinking was that spliced writes without tmp pages would be > fastest, then non-splice writes w/out tmp pages and spliced writes w/ > would be roughly the same. But i'd need to benchmark and verify this > assumption. >=20 A somewhat related question: is Bernd's io_uring patchset susceptible to the same problem as splice() in this situation? IOW, does the kernel inline pagecache pages into the io_uring buffers? If it doesn't have the same issue, then maybe we should think about using that to make a clean behavior break. Gate large folios and not using bounce pages behind io_uring. That would mean dealing with multiple IO paths, but that might still be simpler than trying to deal with multiple folio sizes in the writeback rbtree tracking. > >=20 > > > - codewise, imo this gets messy (eg we would still need the rb tree > > > and would now need to check writeback against folio writeback state > > > and against the rb tree) > >=20 > > I'm thinking of something slightly different: remove the current tmp > > page mess, but instead of duplicating a page ref on splice, fall back > > to copying the cache page (see the user_pages case in > > fuse_copy_page()). This should have very similar performance to what > > we have today, but allows us to deal with page accesses the same way > > for both regular and splice I/O on /dev/fuse. >=20 > 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? >=20 --=20 Jeff Layton