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[174.109.172.136]) by smtp.gmail.com with ESMTPSA id s186sm1546520qka.98.2021.01.20.07.41.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 20 Jan 2021 07:41:34 -0800 (PST) Subject: Re: [PATCH v4 17/18] btrfs: integrate page status update for data read path into begin/end_page_read() To: Qu Wenruo , linux-btrfs@vger.kernel.org References: <20210116071533.105780-1-wqu@suse.com> <20210116071533.105780-18-wqu@suse.com> From: Josef Bacik Message-ID: Date: Wed, 20 Jan 2021 10:41:33 -0500 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 In-Reply-To: <20210116071533.105780-18-wqu@suse.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 1/16/21 2:15 AM, Qu Wenruo wrote: > In btrfs data page read path, the page status update are handled in two > different locations: > > btrfs_do_read_page() > { > while (cur <= end) { > /* No need to read from disk */ > if (HOLE/PREALLOC/INLINE){ > memset(); > set_extent_uptodate(); > continue; > } > /* Read from disk */ > ret = submit_extent_page(end_bio_extent_readpage); > } > > end_bio_extent_readpage() > { > endio_readpage_uptodate_page_status(); > } > > This is fine for sectorsize == PAGE_SIZE case, as for above loop we > should only hit one branch and then exit. > > But for subpage, there are more works to be done in page status update: > - Page Unlock condition > Unlike regular page size == sectorsize case, we can no longer just > unlock a page without a brain. > Only the last reader of the page can unlock the page. > This means, we can unlock the page either in the while() loop, or in > the endio function. > > - Page uptodate condition > Since we have multiple sectors to read for a page, we can only mark > the full page uptodate if all sectors are uptodate. > > To handle both subpage and regular cases, introduce a pair of functions > to help handling page status update: > > - being_page_read() > For regular case, it does nothing. > For subpage case, it update the reader counters so that later > end_page_read() can know who is the last one to unlock the page. > > - end_page_read() > This is just endio_readpage_uptodate_page_status() renamed. > The original name is a little too long and too specific for endio. > > The only new trick added is the condition for page unlock. > Now for subage data, we unlock the page if we're the last reader. > > This does not only provide the basis for subpage data read, but also > hide the special handling of page read from the main read loop. > > Signed-off-by: Qu Wenruo > --- > fs/btrfs/extent_io.c | 38 +++++++++++++++++++---------- > fs/btrfs/subpage.h | 57 +++++++++++++++++++++++++++++++++++--------- > 2 files changed, 72 insertions(+), 23 deletions(-) > > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c > index 4bce03fed205..6ae820144ec7 100644 > --- a/fs/btrfs/extent_io.c > +++ b/fs/btrfs/extent_io.c > @@ -2839,8 +2839,17 @@ static void endio_readpage_release_extent(struct processed_extent *processed, > processed->uptodate = uptodate; > } > > -static void endio_readpage_update_page_status(struct page *page, bool uptodate, > - u64 start, u32 len) > +static void begin_data_page_read(struct btrfs_fs_info *fs_info, struct page *page) > +{ > + ASSERT(PageLocked(page)); > + if (fs_info->sectorsize == PAGE_SIZE) > + return; > + > + ASSERT(PagePrivate(page)); > + btrfs_subpage_start_reader(fs_info, page, page_offset(page), PAGE_SIZE); > +} > + > +static void end_page_read(struct page *page, bool uptodate, u64 start, u32 len) > { > struct btrfs_fs_info *fs_info = btrfs_sb(page->mapping->host->i_sb); > > @@ -2856,7 +2865,12 @@ static void endio_readpage_update_page_status(struct page *page, bool uptodate, > > if (fs_info->sectorsize == PAGE_SIZE) > unlock_page(page); > - /* Subpage locking will be handled in later patches */ > + else if (is_data_inode(page->mapping->host)) > + /* > + * For subpage data, unlock the page if we're the last reader. > + * For subpage metadata, page lock is not utilized for read. > + */ > + btrfs_subpage_end_reader(fs_info, page, start, len); > } > > /* > @@ -2993,7 +3007,7 @@ static void end_bio_extent_readpage(struct bio *bio) > bio_offset += len; > > /* Update page status and unlock */ > - endio_readpage_update_page_status(page, uptodate, start, len); > + end_page_read(page, uptodate, start, len); > endio_readpage_release_extent(&processed, BTRFS_I(inode), > start, end, uptodate); > } > @@ -3267,6 +3281,7 @@ int btrfs_do_readpage(struct page *page, struct extent_map **em_cached, > unsigned int read_flags, u64 *prev_em_start) > { > struct inode *inode = page->mapping->host; > + struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb); > u64 start = page_offset(page); > const u64 end = start + PAGE_SIZE - 1; > u64 cur = start; > @@ -3310,6 +3325,7 @@ int btrfs_do_readpage(struct page *page, struct extent_map **em_cached, > kunmap_atomic(userpage); > } > } > + begin_data_page_read(fs_info, page); > while (cur <= end) { > bool force_bio_submit = false; > u64 disk_bytenr; > @@ -3327,13 +3343,14 @@ int btrfs_do_readpage(struct page *page, struct extent_map **em_cached, > &cached, GFP_NOFS); > unlock_extent_cached(tree, cur, > cur + iosize - 1, &cached); > + end_page_read(page, true, cur, iosize); > break; > } > em = __get_extent_map(inode, page, pg_offset, cur, > end - cur + 1, em_cached); > if (IS_ERR_OR_NULL(em)) { > - SetPageError(page); > unlock_extent(tree, cur, end); > + end_page_read(page, false, cur, end + 1 - cur); > break; > } > extent_offset = cur - em->start; > @@ -3416,6 +3433,7 @@ int btrfs_do_readpage(struct page *page, struct extent_map **em_cached, > &cached, GFP_NOFS); > unlock_extent_cached(tree, cur, > cur + iosize - 1, &cached); > + end_page_read(page, true, cur, iosize); > cur = cur + iosize; > pg_offset += iosize; > continue; > @@ -3425,6 +3443,7 @@ int btrfs_do_readpage(struct page *page, struct extent_map **em_cached, > EXTENT_UPTODATE, 1, NULL)) { > check_page_uptodate(tree, page); > unlock_extent(tree, cur, cur + iosize - 1); > + end_page_read(page, true, cur, iosize); > cur = cur + iosize; > pg_offset += iosize; > continue; > @@ -3433,8 +3452,8 @@ int btrfs_do_readpage(struct page *page, struct extent_map **em_cached, > * to date. Error out > */ > if (block_start == EXTENT_MAP_INLINE) { > - SetPageError(page); > unlock_extent(tree, cur, cur + iosize - 1); > + end_page_read(page, false, cur, iosize); > cur = cur + iosize; > pg_offset += iosize; > continue; > @@ -3451,19 +3470,14 @@ int btrfs_do_readpage(struct page *page, struct extent_map **em_cached, > nr++; > *bio_flags = this_bio_flag; > } else { > - SetPageError(page); > unlock_extent(tree, cur, cur + iosize - 1); > + end_page_read(page, false, cur, iosize); > goto out; > } > cur = cur + iosize; > pg_offset += iosize; > } > out: > - if (!nr) { > - if (!PageError(page)) > - SetPageUptodate(page); > - unlock_page(page); > - } Huh? Now in the normal case we're not getting an unlocked page. Not only that we're not setting it uptodate if we had to 0 the whole page, so we're just left dangling here because the endio will never be called. Not to mention you're deleting all of teh SetPageError() calls for no reason that I can see, and not replacing it with anything else, so you've essentially ripped out any error handling on memory allocation. Thanks, Josef