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Message-ID: <20110213012528.GD19533@dhcp231-156.rdu.redhat.com>
Date: Sat, 12 Feb 2011 20:25:29 -0500
From: Josef Bacik <josef@...hat.com>
To: "Theodore Ts'o" <tytso@....edu>
Cc: Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH,RFC 1/7] ext4: fold __mpage_da_writepage() into
write_cache_pages_da()
On Sat, Feb 12, 2011 at 07:15:51PM -0500, Theodore Ts'o wrote:
> Fold the __mpage_da_writepage() function into write_cache_pages_da().
> This will give us opportunities to clean up and simplify the resulting
> code.
>
> Signed-off-by: "Theodore Ts'o" <tytso@....edu>
> ---
> fs/ext4/inode.c | 206 ++++++++++++++++++++++++-------------------------------
> 1 files changed, 91 insertions(+), 115 deletions(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 9f7f9e4..627729f 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -2438,102 +2438,6 @@ static int ext4_bh_delay_or_unwritten(handle_t *handle, struct buffer_head *bh)
> }
>
> /*
> - * __mpage_da_writepage - finds extent of pages and blocks
> - *
> - * @page: page to consider
> - * @wbc: not used, we just follow rules
> - * @data: context
> - *
> - * The function finds extents of pages and scan them for all blocks.
> - */
> -static int __mpage_da_writepage(struct page *page,
> - struct writeback_control *wbc,
> - struct mpage_da_data *mpd)
> -{
> - struct inode *inode = mpd->inode;
> - struct buffer_head *bh, *head;
> - sector_t logical;
> -
> - /*
> - * Can we merge this page to current extent?
> - */
> - if (mpd->next_page != page->index) {
> - /*
> - * Nope, we can't. So, we map non-allocated blocks
> - * and start IO on them
> - */
> - if (mpd->next_page != mpd->first_page) {
> - mpage_da_map_and_submit(mpd);
> - /*
> - * skip rest of the page in the page_vec
> - */
> - redirty_page_for_writepage(wbc, page);
> - unlock_page(page);
> - return MPAGE_DA_EXTENT_TAIL;
> - }
> -
> - /*
> - * Start next extent of pages ...
> - */
> - mpd->first_page = page->index;
> -
> - /*
> - * ... and blocks
> - */
> - mpd->b_size = 0;
> - mpd->b_state = 0;
> - mpd->b_blocknr = 0;
> - }
> -
> - mpd->next_page = page->index + 1;
> - logical = (sector_t) page->index <<
> - (PAGE_CACHE_SHIFT - inode->i_blkbits);
> -
> - if (!page_has_buffers(page)) {
> - mpage_add_bh_to_extent(mpd, logical, PAGE_CACHE_SIZE,
> - (1 << BH_Dirty) | (1 << BH_Uptodate));
> - if (mpd->io_done)
> - return MPAGE_DA_EXTENT_TAIL;
> - } else {
> - /*
> - * Page with regular buffer heads, just add all dirty ones
> - */
> - head = page_buffers(page);
> - bh = head;
> - do {
> - BUG_ON(buffer_locked(bh));
> - /*
> - * We need to try to allocate
> - * unmapped blocks in the same page.
> - * Otherwise we won't make progress
> - * with the page in ext4_writepage
> - */
> - if (ext4_bh_delay_or_unwritten(NULL, bh)) {
> - mpage_add_bh_to_extent(mpd, logical,
> - bh->b_size,
> - bh->b_state);
> - if (mpd->io_done)
> - return MPAGE_DA_EXTENT_TAIL;
> - } else if (buffer_dirty(bh) && (buffer_mapped(bh))) {
> - /*
> - * mapped dirty buffer. We need to update
> - * the b_state because we look at
> - * b_state in mpage_da_map_blocks. We don't
> - * update b_size because if we find an
> - * unmapped buffer_head later we need to
> - * use the b_state flag of that buffer_head.
> - */
> - if (mpd->b_size == 0)
> - mpd->b_state = bh->b_state & BH_FLAGS;
> - }
> - logical++;
> - } while ((bh = bh->b_this_page) != head);
> - }
> -
> - return 0;
> -}
> -
> -/*
> * This is a special get_blocks_t callback which is used by
> * ext4_da_write_begin(). It will either return mapped block or
> * reserve space for a single block.
> @@ -2811,18 +2715,17 @@ static int ext4_da_writepages_trans_blocks(struct inode *inode)
>
> /*
> * write_cache_pages_da - walk the list of dirty pages of the given
> - * address space and call the callback function (which usually writes
> - * the pages).
> - *
> - * This is a forked version of write_cache_pages(). Differences:
> - * Range cyclic is ignored.
> - * no_nrwrite_index_update is always presumed true
> + * address space and accumulate pages that need writing, and call
> + * mpage_da_map_and_submit to map the pages and then write them.
> */
> static int write_cache_pages_da(struct address_space *mapping,
> struct writeback_control *wbc,
> struct mpage_da_data *mpd,
> pgoff_t *done_index)
> {
> + struct inode *inode = mpd->inode;
> + struct buffer_head *bh, *head;
> + sector_t logical;
> int ret = 0;
> int done = 0;
> struct pagevec pvec;
> @@ -2899,17 +2802,90 @@ continue_unlock:
> if (!clear_page_dirty_for_io(page))
> goto continue_unlock;
>
> - ret = __mpage_da_writepage(page, wbc, mpd);
> - if (unlikely(ret)) {
> - if (ret == AOP_WRITEPAGE_ACTIVATE) {
> + /* BEGIN __mpage_da_writepage */
> +
> + /*
> + * Can we merge this page to current extent?
> + */
> + if (mpd->next_page != page->index) {
> + /*
> + * Nope, we can't. So, we map
> + * non-allocated blocks and start IO
> + * on them
> + */
> + if (mpd->next_page != mpd->first_page) {
> + mpage_da_map_and_submit(mpd);
> + /*
> + * skip rest of the page in the page_vec
> + */
> + redirty_page_for_writepage(wbc, page);
> unlock_page(page);
> - ret = 0;
> - } else {
> - done = 1;
> - break;
> + ret = MPAGE_DA_EXTENT_TAIL;
> + goto out;
> + }
> +
> + /*
> + * Start next extent of pages and blocks
> + */
> + mpd->first_page = page->index;
> + mpd->b_size = 0;
> + mpd->b_state = 0;
> + mpd->b_blocknr = 0;
> + }
> +
> + mpd->next_page = page->index + 1;
> + logical = (sector_t) page->index <<
> + (PAGE_CACHE_SHIFT - inode->i_blkbits);
> +
> + if (!page_has_buffers(page)) {
> + mpage_add_bh_to_extent(mpd, logical, PAGE_CACHE_SIZE,
> + (1 << BH_Dirty) | (1 << BH_Uptodate));
> + if (mpd->io_done) {
> + ret = MPAGE_DA_EXTENT_TAIL;
> + goto out;
> }
> + } else {
> + /*
> + * Page with regular buffer heads, just add all dirty ones
> + */
> + head = page_buffers(page);
> + bh = head;
> + do {
> + BUG_ON(buffer_locked(bh));
> + /*
> + * We need to try to allocate
> + * unmapped blocks in the same page.
> + * Otherwise we won't make progress
> + * with the page in ext4_writepage
> + */
> + if (ext4_bh_delay_or_unwritten(NULL, bh)) {
> + mpage_add_bh_to_extent(mpd, logical,
> + bh->b_size,
> + bh->b_state);
> + if (mpd->io_done) {
> + ret = MPAGE_DA_EXTENT_TAIL;
> + goto out;
> + }
> + } else if (buffer_dirty(bh) && (buffer_mapped(bh))) {
> + /*
> + * mapped dirty buffer. We need to update
> + * the b_state because we look at
> + * b_state in mpage_da_map_blocks. We don't
> + * update b_size because if we find an
> + * unmapped buffer_head later we need to
> + * use the b_state flag of that buffer_head.
> + */
> + if (mpd->b_size == 0)
> + mpd->b_state = bh->b_state & BH_FLAGS;
> + }
> + logical++;
> + } while ((bh = bh->b_this_page) != head);
> }
>
> + ret = 0;
> +
> + /* END __mpage_da_writepage */
> +
> if (nr_to_write > 0) {
> nr_to_write--;
> if (nr_to_write == 0 &&
> @@ -2933,6 +2909,10 @@ continue_unlock:
> cond_resched();
> }
> return ret;
> +out:
> + pagevec_release(&pvec);
> + cond_resched();
> + return ret;
> }
Do we really need the cond_resched() here? Seems like it will just add
unwanted/uneeded latencies. Thanks,
Josef
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