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 1133B19884C; Wed, 5 Feb 2025 19:10:17 +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=1738782619; cv=none; b=X7UII/44MS5JPfVPyWNaDR6mbC1gv7xcxmlF138LY3+qQ6MwZEYQlTAKYfpfyBsDK+MrSvqpkuYl+63Ob4nQMZBM1/H+eYfXe4CTnjUPKNy+Ii8H5qsLgMOEF5MNmNhGp9Wn+QMBhIx/K3fRn3eahRSlV1cRNaqq5P8uWV07csc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738782619; c=relaxed/simple; bh=Q5NpPJTWiZxxRDtrcQlp6qi1NFM2KizHLpBPnRARTAA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=FbvkPN7wvgajYkQqw1hA5iRgQdE5b89xRCgedLeaGYQttcOH7lIJQamcU9D3HaYkZiZ3mWtiaSP7SF+fRIpctC5NuTrMqkxIGAlS3Rm/LhyhWX3e0+viHSbyb9OdH3dPmimM6t4fU/8xM6zKY9BriQz7AWRQ+dBW8INT6RrJzmI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=V4HyoKcF; 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="V4HyoKcF" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6BD3AC4CED1; Wed, 5 Feb 2025 19:10:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1738782617; bh=Q5NpPJTWiZxxRDtrcQlp6qi1NFM2KizHLpBPnRARTAA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=V4HyoKcFXPDvF9kxw1cidDOlHooXOs6Wj9auCa104IKVJO/SxUO5prxLkP3cgdyYc hgSS2Jhm/XjEM3eDIINSoOhM+Exb4h+juMltmSynIrxJTvjab3xZwt9WvXryLBqL9/ LxdT3nWqeFfkjI4SdwxglsUdOqGgylpIL/+oZK4zbOVceesX4MM3h61/T68Uuh2o6w Zs5++f6udoNd6pvrUNH2izuHCbE1lRftn7oZ9Ou9DFd+bYoAh20U5sUlk5pgiC4z0a mSHrEnXQ75/GwaYkrWvnE0l0k8SlVlD21VL00AuYxDl6tBAqTF6iKpZiHkT8WD7W3l Sk9VNkhPYzE/g== Date: Wed, 5 Feb 2025 11:10:16 -0800 From: "Darrick J. Wong" To: Brian Foster Cc: linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org, Christoph Hellwig Subject: Re: [PATCH v5 07/10] iomap: support incremental iomap_iter advances Message-ID: <20250205191016.GQ21808@frogsfrogsfrogs> References: <20250205135821.178256-1-bfoster@redhat.com> <20250205135821.178256-8-bfoster@redhat.com> Precedence: bulk X-Mailing-List: linux-xfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250205135821.178256-8-bfoster@redhat.com> On Wed, Feb 05, 2025 at 08:58:18AM -0500, Brian Foster wrote: > The current iomap_iter iteration model reads the mapping from the > filesystem, processes the subrange of the operation associated with > the current mapping, and returns the number of bytes processed back > to the iteration code. The latter advances the position and > remaining length of the iter in preparation for the next iteration. > > At the _iter() handler level, this tends to produce a processing > loop where the local code pulls the current position and remaining > length out of the iter, iterates it locally based on file offset, > and then breaks out when the associated range has been fully > processed. > > This works well enough for current handlers, but upcoming > enhancements require a bit more flexibility in certain situations. > Enhancements for zero range will lead to a situation where the > processing loop is no longer a pure ascending offset walk, but > rather dictated by pagecache state and folio lookup. Since folio > lookup and write preparation occur at different levels, it is more > difficult to manage position and length outside of the iter. > > To provide more flexibility to certain iomap operations, introduce > support for incremental iomap_iter advances from within the > operation itself. This allows more granular advances for operations > that might not use the typical file offset based walk. > > Note that the semantics for operations that use incremental advances > is slightly different than traditional operations. Operations that > advance the iter directly are expected to return success or failure > (i.e. 0 or negative error code) in iter.processed rather than the > number of bytes processed. I think this needs to be documented in the code comments for @processed in iomap.h: * @processed: The iteration loop body should set this to a negative * errno if an error occurs during processing; zero if it advanced * the iter itself with iomap_iter_advance; or the number of bytes * processed if it needs iomap_iter to advance the iter. --D > Signed-off-by: Brian Foster > Reviewed-by: Christoph Hellwig > --- > fs/iomap/iter.c | 32 +++++++++++++++++++++++++------- > include/linux/iomap.h | 3 +++ > 2 files changed, 28 insertions(+), 7 deletions(-) > > diff --git a/fs/iomap/iter.c b/fs/iomap/iter.c > index cdba24dbbfd7..9273ef36d5ae 100644 > --- a/fs/iomap/iter.c > +++ b/fs/iomap/iter.c > @@ -35,6 +35,8 @@ static inline void iomap_iter_done(struct iomap_iter *iter) > WARN_ON_ONCE(iter->iomap.offset + iter->iomap.length <= iter->pos); > WARN_ON_ONCE(iter->iomap.flags & IOMAP_F_STALE); > > + iter->iter_start_pos = iter->pos; > + > trace_iomap_iter_dstmap(iter->inode, &iter->iomap); > if (iter->srcmap.type != IOMAP_HOLE) > trace_iomap_iter_srcmap(iter->inode, &iter->srcmap); > @@ -58,6 +60,8 @@ static inline void iomap_iter_done(struct iomap_iter *iter) > int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops) > { > bool stale = iter->iomap.flags & IOMAP_F_STALE; > + ssize_t advanced = iter->processed > 0 ? iter->processed : 0; > + u64 olen = iter->len; > s64 processed; > int ret; > > @@ -66,11 +70,22 @@ int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops) > if (!iter->iomap.length) > goto begin; > > + /* > + * If iter.processed is zero, the op may still have advanced the iter > + * itself. Calculate the advanced and original length bytes based on how > + * far pos has advanced for ->iomap_end(). > + */ > + if (!advanced) { > + advanced = iter->pos - iter->iter_start_pos; > + olen += advanced; > + } > + > if (ops->iomap_end) { > - ret = ops->iomap_end(iter->inode, iter->pos, iomap_length(iter), > - iter->processed > 0 ? iter->processed : 0, > - iter->flags, &iter->iomap); > - if (ret < 0 && !iter->processed) > + ret = ops->iomap_end(iter->inode, iter->iter_start_pos, > + iomap_length_trim(iter, iter->iter_start_pos, > + olen), > + advanced, iter->flags, &iter->iomap); > + if (ret < 0 && !advanced) > return ret; > } > > @@ -81,8 +96,11 @@ int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops) > } > > /* > - * Advance the iter and clear state from the previous iteration. Use > - * iter->len to determine whether to continue onto the next mapping. > + * Advance the iter and clear state from the previous iteration. This > + * passes iter->processed because that reflects the bytes processed but > + * not yet advanced by the iter handler. > + * > + * Use iter->len to determine whether to continue onto the next mapping. > * Explicitly terminate in the case where the current iter has not > * advanced at all (i.e. no work was done for some reason) unless the > * mapping has been marked stale and needs to be reprocessed. > @@ -90,7 +108,7 @@ int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops) > ret = iomap_iter_advance(iter, &processed); > if (!ret && iter->len > 0) > ret = 1; > - if (ret > 0 && !iter->processed && !stale) > + if (ret > 0 && !advanced && !stale) > ret = 0; > iomap_iter_reset_iomap(iter); > if (ret <= 0) > diff --git a/include/linux/iomap.h b/include/linux/iomap.h > index f304c602e5fe..0135a7f8dd83 100644 > --- a/include/linux/iomap.h > +++ b/include/linux/iomap.h > @@ -211,6 +211,8 @@ struct iomap_ops { > * calls to iomap_iter(). Treat as read-only in the body. > * @len: The remaining length of the file segment we're operating on. > * It is updated at the same time as @pos. > + * @iter_start_pos: The original start pos for the current iomap. Used for > + * incremental iter advance. > * @processed: The number of bytes processed by the body in the most recent > * iteration, or a negative errno. 0 causes the iteration to stop. > * @flags: Zero or more of the iomap_begin flags above. > @@ -221,6 +223,7 @@ struct iomap_iter { > struct inode *inode; > loff_t pos; > u64 len; > + loff_t iter_start_pos; > s64 processed; > unsigned flags; > struct iomap iomap; > -- > 2.48.1 > >