From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 41FFE20C00B for ; Mon, 18 Aug 2025 19:27:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755545278; cv=none; b=sgAcBKBqFy0wR+OW7NZR90EtGkfJYo/L3h/8xQfHInx1ClduMjg2icCN3wIP3nHXv44EDaEbJA5xC+Strt8Nc+BxUYWlMAFKlntKMGVtsuPtsXCs278obDwobop8UwamVgkVSwtAiW92cc7zc6/VjVjhWEGzqxeMbLif8ql/TNo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755545278; c=relaxed/simple; bh=opGCD/JR6Y/SHqLGtRX7sxzmX2B2KsfpnCqz35E93FQ=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=fk8Dy0A0Y4l/egfR47HBa+TgIghNqksViCsvp8ET828NWz5dcOd/uWVJjV+NpH6fSTCMnFjVp4d3TBPK7JCIxnjeybz5lykX/47/9IG1c0Eyx+am+4D07GWXKdiHGwgPOwLm3dZ1roiEqeSV7okCby4mB1Fm4S4LY05jb2wFUsk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Mkw8dSf+; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Mkw8dSf+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6EAA8C4CEEB; Mon, 18 Aug 2025 19:27:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1755545277; bh=opGCD/JR6Y/SHqLGtRX7sxzmX2B2KsfpnCqz35E93FQ=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=Mkw8dSf+nxa2Nv8dKe6T+ni/6Ku6Jqm9Ijcg/EK3NEqgjVlt6Rmdze5Se/Fi/WdEH imvMi7KnbTsA6XjG1vXY3AK7v259ToOC+MUjLZOSrEdyOXOFHmxfx9K4LTyNro91GP Hd1QSgMZB3X6yJcNG3KrVKA4TUxYKttL0RnXdYKkiTlubM25NQYHJ3HGPslKEa3De+ H+MeJKhO6PNME7Aplv+12EVk0Vrs6pGz5gkN3vc9IOkZKHP8E+gB+dWKGoF8KIIb2k RtO8Frl1Ls6ToGXiDa47s7os4JNGdLLOkgrQWlY9PU6b2ZCosTXEX8QKJxP76KHcDO RbddtZvCNfvtg== Message-ID: Subject: Re: [PATCH v7 5/7] NFSD: issue READs using O_DIRECT even if IO is misaligned From: Jeff Layton To: Mike Snitzer Cc: Chuck Lever , linux-nfs@vger.kernel.org Date: Mon, 18 Aug 2025 15:27:56 -0400 In-Reply-To: References: <20250815144607.50967-1-snitzer@kernel.org> <20250815144607.50967-6-snitzer@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV 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Snitzer wrote: > > > If NFSD_IO_DIRECT is used, expand any misaligned READ to the next > > > DIO-aligned block (on either end of the READ). The expanded READ is > > > verified to have proper offset/len (logical_block_size) and > > > dma_alignment checking. > > >=20 > > > Must allocate and use a bounce-buffer page (called 'start_extra_page'= ) > > > if/when expanding the misaligned READ requires reading extra partial > > > page at the start of the READ so that its DIO-aligned. Otherwise that > > > extra page at the start will make its way back to the NFS client and > > > corruption will occur. As found, and then this fix of using an extra > > > page verified, using the 'dt' utility: > > > dt of=3D/mnt/share1/dt_a.test passes=3D1 bs=3D47008 count=3D2 \ > > > iotype=3Dsequential pattern=3Diot onerr=3Dabort oncerr=3Dabort > > > see: https://github.com/RobinTMiller/dt.git > > >=20 > > > Any misaligned READ that is less than 32K won't be expanded to be > > > DIO-aligned (this heuristic just avoids excess work, like allocating > > > start_extra_page, for smaller IO that can generally already perform > > > well using buffered IO). > > >=20 > > > Suggested-by: Jeff Layton > > > Suggested-by: Chuck Lever > > > Signed-off-by: Mike Snitzer > > > --- > > > fs/nfsd/vfs.c | 200 +++++++++++++++++++++++++++++++++++= -- > > > include/linux/sunrpc/svc.h | 5 +- > > > 2 files changed, 194 insertions(+), 11 deletions(-) > > >=20 > > > diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c > > > index c340708fbab4d..64732dc8985d6 100644 > > > --- a/fs/nfsd/vfs.c > > > +++ b/fs/nfsd/vfs.c > > > @@ -19,6 +19,7 @@ > > > #include > > > #include > > > #include > > > +#include > > > #include > > > #include > > > #include > > > @@ -1073,6 +1074,153 @@ __be32 nfsd_splice_read(struct svc_rqst *rqst= p, struct svc_fh *fhp, > > > return nfsd_finish_read(rqstp, fhp, file, offset, count, eof, host_= err); > > > } > > > =20 > > > +struct nfsd_read_dio { > > > + loff_t start; > > > + loff_t end; > > > + unsigned long start_extra; > > > + unsigned long end_extra; > > > + struct page *start_extra_page; > > > +}; > > > + > > > +static void init_nfsd_read_dio(struct nfsd_read_dio *read_dio) > > > +{ > > > + memset(read_dio, 0, sizeof(*read_dio)); > > > + read_dio->start_extra_page =3D NULL; > > > +} > > > + > > > +#define NFSD_READ_DIO_MIN_KB (32 << 10) > > > + > > > +static bool nfsd_analyze_read_dio(struct svc_rqst *rqstp, struct svc= _fh *fhp, > > > + struct nfsd_file *nf, loff_t offset, > > > + unsigned long len, unsigned int base, > > > + struct nfsd_read_dio *read_dio) > > > +{ > > > + const u32 dio_blocksize =3D nf->nf_dio_read_offset_align; > > > + loff_t middle_end, orig_end =3D offset + len; > > > + > > > + if (WARN_ONCE(!nf->nf_dio_mem_align || !nf->nf_dio_read_offset_alig= n, > > > + "%s: underlying filesystem has not provided DIO alignment in= fo\n", > > > + __func__)) > > > + return false; > > > + if (WARN_ONCE(dio_blocksize > PAGE_SIZE, > > > + "%s: underlying storage's dio_blocksize=3D%u > PAGE_SIZE=3D%= lu\n", > > > + __func__, dio_blocksize, PAGE_SIZE)) > > > + return false; > > > + > > > + /* Return early if IO is irreparably misaligned (len < PAGE_SIZE, > > > + * or base not aligned). > > > + * Ondisk alignment is implied by the following code that expands > > > + * misaligned IO to have a DIO-aligned offset and len. > > > + */ > > > + if (unlikely(len < dio_blocksize) || ((base & (nf->nf_dio_mem_align= -1)) !=3D 0)) > > > + return false; > >=20 > > The small len check makes sense, but "base" at this point is the offset > > into the first page. Here you're bailing out early if that's not > > aligned. Isn't that contrary to what this patch is supposed to do > > (which is expand the range so that the I/O is aligned)? >=20 > No matter whether we're expanding the read or not (that's a means to > make the area read from disk DIO-aligned): the memory alignment is > what it is -- so it isn't something that we can change (not without an > extra copy). But thankfully with RDMA the memory for the READ payload > is generally always aligned. >=20 > Chcuk did say in reply to an earlier version of this patchset > (paraphrasing, rather not go splunking in the linux-nfs archive to > find it): a future improvement would be to make sure the READ > payload's memory is always aligned. >=20 Oh right, I got confused between the mem and block alignment here. In light of that, you can add Reviewed-by: Jeff Layton