From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Thu, 31 May 2018 09:45:57 +1000 From: Dave Chinner To: Christoph Hellwig Cc: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 11/13] iomap: add an iomap-based readpage and readpages implementation Message-ID: <20180530234557.GI10363@dastard> References: <20180530095813.31245-1-hch@lst.de> <20180530095813.31245-12-hch@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180530095813.31245-12-hch@lst.de> Sender: owner-linux-mm@kvack.org List-ID: On Wed, May 30, 2018 at 11:58:11AM +0200, Christoph Hellwig wrote: > Simply use iomap_apply to iterate over the file and a submit a bio for > each non-uptodate but mapped region and zero everything else. Note that > as-is this can not be used for file systems with a blocksize smaller than > the page size, but that support will be added later. > > Signed-off-by: Christoph Hellwig > --- > fs/iomap.c | 203 +++++++++++++++++++++++++++++++++++++++++- > include/linux/iomap.h | 4 + > 2 files changed, 206 insertions(+), 1 deletion(-) > > diff --git a/fs/iomap.c b/fs/iomap.c > index b0bc928672af..5e5a266e3325 100644 > --- a/fs/iomap.c > +++ b/fs/iomap.c > @@ -1,6 +1,6 @@ > /* > * Copyright (C) 2010 Red Hat, Inc. > - * Copyright (c) 2016 Christoph Hellwig. > + * Copyright (c) 2016-2018 Christoph Hellwig. > * > * This program is free software; you can redistribute it and/or modify it > * under the terms and conditions of the GNU General Public License, > @@ -18,6 +18,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -102,6 +103,206 @@ iomap_sector(struct iomap *iomap, loff_t pos) > return (iomap->addr + pos - iomap->offset) >> SECTOR_SHIFT; > } > > +static void > +iomap_read_end_io(struct bio *bio) > +{ > + int error = blk_status_to_errno(bio->bi_status); > + struct bio_vec *bvec; > + int i; > + > + bio_for_each_segment_all(bvec, bio, i) > + page_endio(bvec->bv_page, false, error); > + bio_put(bio); > +} > + > +struct iomap_readpage_ctx { > + struct page *cur_page; > + bool cur_page_in_bio; > + bool is_readahead; > + struct bio *bio; > + struct list_head *pages; > +}; > + > +static loff_t > +iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data, > + struct iomap *iomap) > +{ > + struct iomap_readpage_ctx *ctx = data; > + struct page *page = ctx->cur_page; > + unsigned poff = pos & (PAGE_SIZE - 1); > + unsigned plen = min_t(loff_t, PAGE_SIZE - poff, length); > + bool is_contig = false; > + sector_t sector; > + > + /* we don't support blocksize < PAGE_SIZE quite yet: */ sentence ends with a ".". :) > + WARN_ON_ONCE(pos != page_offset(page)); > + WARN_ON_ONCE(plen != PAGE_SIZE); > + > + if (iomap->type != IOMAP_MAPPED || pos >= i_size_read(inode)) { In what situation do we get a read request completely beyond EOF? (comment, please!) > + zero_user(page, poff, plen); > + SetPageUptodate(page); > + goto done; > + } [...] > +int > +iomap_readpage(struct page *page, const struct iomap_ops *ops) > +{ > + struct iomap_readpage_ctx ctx = { .cur_page = page }; > + struct inode *inode = page->mapping->host; > + unsigned poff; > + loff_t ret; > + > + WARN_ON_ONCE(page_has_buffers(page)); > + > + for (poff = 0; poff < PAGE_SIZE; poff += ret) { > + ret = iomap_apply(inode, page_offset(page) + poff, > + PAGE_SIZE - poff, 0, ops, &ctx, > + iomap_readpage_actor); > + if (ret <= 0) { > + WARN_ON_ONCE(ret == 0); > + SetPageError(page); > + break; > + } > + } > + > + if (ctx.bio) { > + submit_bio(ctx.bio); > + WARN_ON_ONCE(!ctx.cur_page_in_bio); > + } else { > + WARN_ON_ONCE(ctx.cur_page_in_bio); > + unlock_page(page); > + } > + return 0; Hmmm. If we had an error from iomap_apply, shouldn't we be returning it here instead just throwing it away? some ->readpage callers appear to ignore the PageError() state on return but do expect errors to be returned. [...] > +iomap_readpages(struct address_space *mapping, struct list_head *pages, > + 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; Two lines, please. > + while (length > 0) { > + ret = iomap_apply(mapping->host, pos, length, 0, ops, > + &ctx, iomap_readpages_actor); > + if (ret <= 0) { > + WARN_ON_ONCE(ret == 0); > + goto done; > + } > + 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); > + put_page(ctx.cur_page); > + } > + WARN_ON_ONCE(!ret && !list_empty(ctx.pages)); What error condition is this warning about? Cheers, Dave. -- Dave Chinner david@fromorbit.com