Messages in this thread | | | Date | Wed, 29 Jan 2020 12:38:39 +1100 | From | Dave Chinner <> | Subject | Re: [PATCH 12/12] iomap: Convert from readpages to readahead |
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On Fri, Jan 24, 2020 at 05:35:53PM -0800, Matthew Wilcox wrote: > From: "Matthew Wilcox (Oracle)" <willy@infradead.org> > > Use the new readahead operation in XFS and iomap. > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> > Cc: linux-xfs@vger.kernel.org
.... > +unsigned > +iomap_readahead(struct address_space *mapping, pgoff_t start, > unsigned nr_pages, const struct iomap_ops *ops) > { > struct iomap_readpage_ctx ctx = { > - .pages = pages, > .is_readahead = true, > }; > - loff_t pos = page_offset(list_entry(pages->prev, struct page, lru)); > - loff_t last = page_offset(list_entry(pages->next, struct page, lru)); > - loff_t length = last - pos + PAGE_SIZE, ret = 0; > + loff_t pos = start * PAGE_SIZE; > + loff_t length = nr_pages * PAGE_SIZE; > > - trace_iomap_readpages(mapping->host, nr_pages); > + trace_iomap_readahead(mapping->host, nr_pages); > > while (length > 0) { > - ret = iomap_apply(mapping->host, pos, length, 0, ops, > - &ctx, iomap_readpages_actor); > + loff_t ret = iomap_apply(mapping->host, pos, length, 0, ops, > + &ctx, iomap_readahead_actor); > if (ret <= 0) { > WARN_ON_ONCE(ret == 0); > - goto done; > + break; > } > pos += ret; > length -= ret; > } > - ret = 0; > -done: > + > if (ctx.bio) > submit_bio(ctx.bio); > - if (ctx.cur_page) { > - if (!ctx.cur_page_in_bio) > - unlock_page(ctx.cur_page); > + if (ctx.cur_page && ctx.cur_page_in_bio) > put_page(ctx.cur_page); > - } > > - /* > - * Check that we didn't lose a page due to the arcance calling > - * conventions.. > - */ > - WARN_ON_ONCE(!ret && !list_empty(ctx.pages)); > - return ret; > + return length / PAGE_SIZE;
Took me quite some time to get my head around whether this was correct or not.
I'm still not certain in the cases where block size != page size and we've got an extent boundary in the middle of the page and had a read error on the second extent in the page. In this case, ctx.cur_page_in_bio is true so we drop the readahead reference to the page. Also, length is not a multiple of page size, and so the nr_pages value returned includes the partial page that we have IO underway on.
That, I think, leads to both a double unlock and a double put_page() of the partial page in question.
Cheers,
Dave. -- Dave Chinner david@fromorbit.com
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