From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx3-rdu2.redhat.com ([66.187.233.73]:50568 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752730AbeGCMb3 (ORCPT ); Tue, 3 Jul 2018 08:31:29 -0400 Date: Tue, 3 Jul 2018 08:31:27 -0400 From: Brian Foster To: Christoph Hellwig Cc: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 20/22] iomap: add support for sub-pagesize buffered I/O without buffer heads Message-ID: <20180703123127.GA22789@bfoster> References: <20180702145813.22496-1-hch@lst.de> <20180702145813.22496-21-hch@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180702145813.22496-21-hch@lst.de> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Mon, Jul 02, 2018 at 08:58:11AM -0600, Christoph Hellwig wrote: > After already supporting a simple implementation of buffered writes for > the blocksize == PAGE_SIZE case in the last commit this adds full support > even for smaller block sizes. There are three bits of per-block > information in the buffer_head structure that really matter for the iomap > read and write path: > > - uptodate status (BH_uptodate) > - marked as currently under read I/O (BH_Async_Read) > - marked as currently under write I/O (BH_Async_Write) > > Instead of having new per-block structures this now adds a per-page > structure called struct iomap_page to track this information in a slightly > different form: > > - a bitmap for the per-block uptodate status. For worst case of a 64k > page size system this bitmap needs to contain 128 bits. For the > typical 4k page size case it only needs 8 bits, although we still > need a full unsigned long due to the way the atomic bitmap API works. > - two atomic_t counters are used to track the outstanding read and write > counts > > There is quite a bit of boilerplate code as the buffered I/O path uses > various helper methods, but the actual code is very straight forward. > > Signed-off-by: Christoph Hellwig > --- > fs/iomap.c | 279 ++++++++++++++++++++++++++++++++++++++---- > include/linux/iomap.h | 31 +++++ > 2 files changed, 289 insertions(+), 21 deletions(-) > > diff --git a/fs/iomap.c b/fs/iomap.c > index 13cdcf33e6c0..ea1b1ba61ba3 100644 > --- a/fs/iomap.c > +++ b/fs/iomap.c ... > @@ -161,13 +295,13 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data, > return PAGE_SIZE; > } > > - /* we don't support blocksize < PAGE_SIZE quite yet. */ > - WARN_ON_ONCE(pos != page_offset(page)); > - WARN_ON_ONCE(plen != PAGE_SIZE); > + iomap_adjust_read_range(inode, iop, &pos, length, &poff, &plen); > + if (plen == 0) > + goto done; > I think the i_size check confused me in the previous go around. It's obviously clear to me now after the iomap zeroing issue and fix, but a one-liner comment couldn't hurt for future reference: /* zero post-eof blocks as the page may be mapped */ That nit aside, this looks good to me and survives my tests: Reviewed-by: Brian Foster > if (iomap->type != IOMAP_MAPPED || pos >= i_size_read(inode)) { > zero_user(page, poff, plen); > - SetPageUptodate(page); > + iomap_set_range_uptodate(page, poff, plen); > goto done; > } > > @@ -183,6 +317,14 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data, > is_contig = true; > } > > + /* > + * If we start a new segment we need to increase the read count, and we > + * need to do so before submitting any previous full bio to make sure > + * that we don't prematurely unlock the page. > + */ > + if (iop) > + atomic_inc(&iop->read_count); > + > if (!ctx->bio || !is_contig || bio_full(ctx->bio)) { > gfp_t gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL); > int nr_vecs = (length + PAGE_SIZE - 1) >> PAGE_SHIFT; > @@ -203,7 +345,13 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data, > > __bio_add_page(ctx->bio, page, plen, poff); > done: > - return plen; > + /* > + * Move the caller beyond our range so that it keeps making progress. > + * For that we have to include any leading non-uptodate ranges, but > + * we can skip trailing ones as they will be handled in the next > + * iteration. > + */ > + return pos - orig_pos + plen; > } > > int > @@ -214,8 +362,6 @@ iomap_readpage(struct page *page, const struct iomap_ops *ops) > 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, > @@ -341,6 +487,84 @@ iomap_readpages(struct address_space *mapping, struct list_head *pages, > } > EXPORT_SYMBOL_GPL(iomap_readpages); > > +int > +iomap_is_partially_uptodate(struct page *page, unsigned long from, > + unsigned long count) > +{ > + struct iomap_page *iop = to_iomap_page(page); > + struct inode *inode = page->mapping->host; > + unsigned first = from >> inode->i_blkbits; > + unsigned last = (from + count - 1) >> inode->i_blkbits; > + unsigned i; > + > + if (iop) { > + for (i = first; i <= last; i++) > + if (!test_bit(i, iop->uptodate)) > + return 0; > + return 1; > + } > + > + return 0; > +} > +EXPORT_SYMBOL_GPL(iomap_is_partially_uptodate); > + > +int > +iomap_releasepage(struct page *page, gfp_t gfp_mask) > +{ > + /* > + * mm accommodates an old ext3 case where clean pages might not have had > + * the dirty bit cleared. Thus, it can send actual dirty pages to > + * ->releasepage() via shrink_active_list(), skip those here. > + */ > + if (PageDirty(page) || PageWriteback(page)) > + return 0; > + iomap_page_release(page); > + return 1; > +} > +EXPORT_SYMBOL_GPL(iomap_releasepage); > + > +void > +iomap_invalidatepage(struct page *page, unsigned int offset, unsigned int len) > +{ > + /* > + * If we are invalidating the entire page, clear the dirty state from it > + * and release it to avoid unnecessary buildup of the LRU. > + */ > + if (offset == 0 && len == PAGE_SIZE) { > + WARN_ON_ONCE(PageWriteback(page)); > + cancel_dirty_page(page); > + iomap_page_release(page); > + } > +} > +EXPORT_SYMBOL_GPL(iomap_invalidatepage); > + > +#ifdef CONFIG_MIGRATION > +int > +iomap_migrate_page(struct address_space *mapping, struct page *newpage, > + struct page *page, enum migrate_mode mode) > +{ > + int ret; > + > + ret = migrate_page_move_mapping(mapping, newpage, page, NULL, mode, 0); > + if (ret != MIGRATEPAGE_SUCCESS) > + return ret; > + > + if (page_has_private(page)) { > + ClearPagePrivate(page); > + set_page_private(newpage, page_private(page)); > + set_page_private(page, 0); > + SetPagePrivate(newpage); > + } > + > + if (mode != MIGRATE_SYNC_NO_COPY) > + migrate_page_copy(newpage, page); > + else > + migrate_page_states(newpage, page); > + return MIGRATEPAGE_SUCCESS; > +} > +EXPORT_SYMBOL_GPL(iomap_migrate_page); > +#endif /* CONFIG_MIGRATION */ > + > static void > iomap_write_failed(struct inode *inode, loff_t pos, unsigned len) > { > @@ -364,6 +588,7 @@ iomap_read_page_sync(struct inode *inode, loff_t block_start, struct page *page, > > if (iomap->type != IOMAP_MAPPED || block_start >= i_size_read(inode)) { > zero_user_segments(page, poff, from, to, poff + plen); > + iomap_set_range_uptodate(page, poff, plen); > return 0; > } > > @@ -379,21 +604,33 @@ static int > __iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, > struct page *page, struct iomap *iomap) > { > + struct iomap_page *iop = iomap_page_create(inode, page); > loff_t block_size = i_blocksize(inode); > loff_t block_start = pos & ~(block_size - 1); > loff_t block_end = (pos + len + block_size - 1) & ~(block_size - 1); > - unsigned poff = block_start & (PAGE_SIZE - 1); > - unsigned plen = min_t(loff_t, PAGE_SIZE - poff, block_end - block_start); > - unsigned from = pos & (PAGE_SIZE - 1), to = from + len; > - > - WARN_ON_ONCE(i_blocksize(inode) < PAGE_SIZE); > + unsigned from = pos & (PAGE_SIZE - 1), to = from + len, poff, plen; > + int status = 0; > > if (PageUptodate(page)) > return 0; > - if (from <= poff && to >= poff + plen) > - return 0; > - return iomap_read_page_sync(inode, block_start, page, > - poff, plen, from, to, iomap); > + > + do { > + iomap_adjust_read_range(inode, iop, &block_start, > + block_end - block_start, &poff, &plen); > + if (plen == 0) > + break; > + > + if ((from > poff && from < poff + plen) || > + (to > poff && to < poff + plen)) { > + status = iomap_read_page_sync(inode, block_start, page, > + poff, plen, from, to, iomap); > + if (status) > + break; > + } > + > + } while ((block_start += plen) < block_end); > + > + return status; > } > > static int > @@ -476,7 +713,7 @@ __iomap_write_end(struct inode *inode, loff_t pos, unsigned len, > if (unlikely(copied < len && !PageUptodate(page))) { > copied = 0; > } else { > - SetPageUptodate(page); > + iomap_set_range_uptodate(page, pos & (PAGE_SIZE - 1), len); > iomap_set_page_dirty(page); > } > return __generic_write_end(inode, pos, copied, page); > @@ -812,7 +1049,7 @@ iomap_page_mkwrite_actor(struct inode *inode, loff_t pos, loff_t length, > block_commit_write(page, 0, length); > } else { > WARN_ON_ONCE(!PageUptodate(page)); > - WARN_ON_ONCE(i_blocksize(inode) < PAGE_SIZE); > + iomap_page_create(inode, page); > } > > return length; > diff --git a/include/linux/iomap.h b/include/linux/iomap.h > index 5eb9ca8d7ce5..3555d54bf79a 100644 > --- a/include/linux/iomap.h > +++ b/include/linux/iomap.h > @@ -2,6 +2,9 @@ > #ifndef LINUX_IOMAP_H > #define LINUX_IOMAP_H 1 > > +#include > +#include > +#include > #include > > struct address_space; > @@ -98,12 +101,40 @@ struct iomap_ops { > ssize_t written, unsigned flags, struct iomap *iomap); > }; > > +/* > + * Structure allocate for each page when block size < PAGE_SIZE to track > + * sub-page uptodate status and I/O completions. > + */ > +struct iomap_page { > + atomic_t read_count; > + atomic_t write_count; > + DECLARE_BITMAP(uptodate, PAGE_SIZE / 512); > +}; > + > +static inline struct iomap_page *to_iomap_page(struct page *page) > +{ > + if (page_has_private(page)) > + return (struct iomap_page *)page_private(page); > + return NULL; > +} > + > ssize_t iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *from, > const struct iomap_ops *ops); > int iomap_readpage(struct page *page, const struct iomap_ops *ops); > int iomap_readpages(struct address_space *mapping, struct list_head *pages, > unsigned nr_pages, const struct iomap_ops *ops); > int iomap_set_page_dirty(struct page *page); > +int iomap_is_partially_uptodate(struct page *page, unsigned long from, > + unsigned long count); > +int iomap_releasepage(struct page *page, gfp_t gfp_mask); > +void iomap_invalidatepage(struct page *page, unsigned int offset, > + unsigned int len); > +#ifdef CONFIG_MIGRATION > +int iomap_migrate_page(struct address_space *mapping, struct page *newpage, > + struct page *page, enum migrate_mode mode); > +#else > +#define iomap_migrate_page NULL > +#endif > int iomap_file_dirty(struct inode *inode, loff_t pos, loff_t len, > const struct iomap_ops *ops); > int iomap_zero_range(struct inode *inode, loff_t pos, loff_t len, > -- > 2.18.0 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html