From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from userp2120.oracle.com ([156.151.31.85]:40092 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753179AbeGCVwu (ORCPT ); Tue, 3 Jul 2018 17:52:50 -0400 Date: Tue, 3 Jul 2018 14:52:32 -0700 From: "Darrick J. Wong" To: Brian Foster Cc: Christoph Hellwig , 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: <20180703215232.GW32415@magnolia> References: <20180702145813.22496-1-hch@lst.de> <20180702145813.22496-21-hch@lst.de> <20180703123127.GA22789@bfoster> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180703123127.GA22789@bfoster> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Tue, Jul 03, 2018 at 08:31:27AM -0400, Brian Foster wrote: > 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 Looks ok, will insert the comment on its way in. Will test (again)... Reviewed-by: Darrick J. Wong --D > > > 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 > -- > 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