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Date: Wed, 19 Feb 2020 09:06:42 -0800 From: Matthew Wilcox <willy@...radead.org> To: Dave Chinner <david@...morbit.com> Cc: linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org, linux-btrfs@...r.kernel.org, linux-erofs@...ts.ozlabs.org, linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net, cluster-devel@...hat.com, ocfs2-devel@....oracle.com, linux-xfs@...r.kernel.org Subject: Re: [PATCH v6 17/19] iomap: Restructure iomap_readpages_actor On Wed, Feb 19, 2020 at 05:40:05PM +1100, Dave Chinner wrote: > Ok, that's what the ctx.cur_page_in_bio check is used to detect i.e. > if we've got a page that the readahead cursor points at, and we > haven't actually added it to a bio, then we can leave it to the > read_pages() to unlock and clean up. If it's in a bio, then IO > completion will unlock it and so we only have to drop the submission > reference and move the readahead cursor forwards so read_pages() > doesn't try to unlock this page. i.e: > > /* clean up partial page submission failures */ > if (ctx.cur_page && ctx.cur_page_in_bio) { > put_page(ctx.cur_page); > readahead_next(rac); > } > > looks to me like it will handle the case of "ret == 0" in the actor > function just fine. Here's what I ended up with: @@ -400,15 +400,9 @@ iomap_readpages_actor(struct inode *inode, loff_t pos, loff_t length, void *data, struct iomap *iomap, struct iomap *srcmap) { struct iomap_readpage_ctx *ctx = data; - loff_t done, ret; - - for (done = 0; done < length; done += ret) { - if (ctx->cur_page && offset_in_page(pos + done) == 0) { - if (!ctx->cur_page_in_bio) - unlock_page(ctx->cur_page); - put_page(ctx->cur_page); - ctx->cur_page = NULL; - } + loff_t ret, done = 0; + + while (done < length) { if (!ctx->cur_page) { ctx->cur_page = iomap_next_page(inode, ctx->pages, pos, length, &done); @@ -418,6 +412,20 @@ iomap_readpages_actor(struct inode *inode, loff_t pos, loff_t length, } ret = iomap_readpage_actor(inode, pos + done, length - done, ctx, iomap, srcmap); + done += ret; + + /* Keep working on a partial page */ + if (ret && offset_in_page(pos + done)) + continue; + + if (!ctx->cur_page_in_bio) + unlock_page(ctx->cur_page); + put_page(ctx->cur_page); + ctx->cur_page = NULL; + + /* Don't loop forever if we made no progress */ + if (WARN_ON(!ret)) + break; } return done; @@ -451,11 +459,7 @@ iomap_readpages(struct address_space *mapping, struct list_head *pages, done: if (ctx.bio) submit_bio(ctx.bio); - if (ctx.cur_page) { - if (!ctx.cur_page_in_bio) - unlock_page(ctx.cur_page); - put_page(ctx.cur_page); - } + BUG_ON(ctx.cur_page); /* * Check that we didn't lose a page due to the arcance calling so we'll WARN if we get a ret == 0 (matching ->readpage), and we'll BUG if we ever see a page being leaked out of readpages_actor, which is a thing that should never happen and we definitely want to be noisy about if it does.
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