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Date: Sat, 11 Oct 2008 12:51:52 +0200
From: Nick Piggin <npiggin@...e.de>
To: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc: cmm@...ibm.com, tytso@....edu, sandeen@...hat.com,
chris.mason@...cle.com, akpm@...ux-foundation.org,
hch@...radead.org, steve@...gwyn.com, mpatocka@...hat.com,
linux-mm@...ck.org, inux-fsdevel@...r.kernel.org,
linux-ext4@...r.kernel.org
Subject: Re: [PATCH updated] ext4: Fix file fragmentation during large file write.
On Fri, Oct 10, 2008 at 11:32:56PM +0530, Aneesh Kumar K.V wrote:
> The range_cyclic writeback mode use the address_space
> writeback_index as the start index for writeback. With
> delayed allocation we were updating writeback_index
> wrongly resulting in highly fragmented file. Number of
> extents reduced from 4000 to 27 for a 3GB file with
> the below patch.
>
> The patch also removes the range_cont writeback mode
> added for ext4 delayed allocation. Instead we add
> two new flags in writeback_control which control
> the behaviour of write_cache_pages.
The mm/page-writeback.c changes look OK, although it loks like you've
got rid of range_cont? Should we do a patch to get rid of it entirely
from the tree first?
I don't mind rediffing my patchset on top of this, but this seems smaller
and not strictly a bugfix so I would prefer to go the other way if you
agree.
Seems like it could be broken up into several patches (eg. pagevec_lookup).
The results look very nice.
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> ---
> fs/ext4/inode.c | 110 +++++++++++++++++++++++++-------------------
> include/linux/writeback.h | 5 ++-
> mm/page-writeback.c | 11 +++--
> 3 files changed, 73 insertions(+), 53 deletions(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 7c2820e..f8890b9 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -1648,6 +1648,7 @@ static int mpage_da_submit_io(struct mpage_da_data *mpd)
> int ret = 0, err, nr_pages, i;
> unsigned long index, end;
> struct pagevec pvec;
> + long pages_skipped;
>
> BUG_ON(mpd->next_page <= mpd->first_page);
> pagevec_init(&pvec, 0);
> @@ -1655,20 +1656,30 @@ static int mpage_da_submit_io(struct mpage_da_data *mpd)
> end = mpd->next_page - 1;
>
> while (index <= end) {
> - /* XXX: optimize tail */
> - nr_pages = pagevec_lookup(&pvec, mapping, index, PAGEVEC_SIZE);
> + /*
> + * We can use PAGECACHE_TAG_DIRTY lookup here because
> + * even though we have cleared the dirty flag on the page
> + * We still keep the page in the radix tree with tag
> + * PAGECACHE_TAG_DIRTY. See clear_page_dirty_for_io.
> + * The PAGECACHE_TAG_DIRTY is cleared in set_page_writeback
> + * which is called via the below writepage callback.
> + */
> + nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
> + PAGECACHE_TAG_DIRTY,
> + min(end - index,
> + (pgoff_t)PAGEVEC_SIZE-1) + 1);
> if (nr_pages == 0)
> break;
> for (i = 0; i < nr_pages; i++) {
> struct page *page = pvec.pages[i];
>
> - index = page->index;
> - if (index > end)
> - break;
> - index++;
> -
> + pages_skipped = mpd->wbc->pages_skipped;
> err = mapping->a_ops->writepage(page, mpd->wbc);
> - if (!err)
> + if (!err && (pages_skipped == mpd->wbc->pages_skipped))
> + /*
> + * have successfully written the page
> + * without skipping the same
> + */
> mpd->pages_written++;
> /*
> * In error case, we have to continue because
> @@ -2104,7 +2115,6 @@ static int mpage_da_writepages(struct address_space *mapping,
> struct writeback_control *wbc,
> struct mpage_da_data *mpd)
> {
> - long to_write;
> int ret;
>
> if (!mpd->get_block)
> @@ -2119,10 +2129,7 @@ static int mpage_da_writepages(struct address_space *mapping,
> mpd->pages_written = 0;
> mpd->retval = 0;
>
> - to_write = wbc->nr_to_write;
> -
> ret = write_cache_pages(mapping, wbc, __mpage_da_writepage, mpd);
> -
> /*
> * Handle last extent of pages
> */
> @@ -2131,7 +2138,7 @@ static int mpage_da_writepages(struct address_space *mapping,
> mpage_da_submit_io(mpd);
> }
>
> - wbc->nr_to_write = to_write - mpd->pages_written;
> + wbc->nr_to_write -= mpd->pages_written;
> return ret;
> }
>
> @@ -2360,12 +2367,14 @@ static int ext4_da_writepages_trans_blocks(struct inode *inode)
> static int ext4_da_writepages(struct address_space *mapping,
> struct writeback_control *wbc)
> {
> + pgoff_t index;
> + int range_whole = 0;
> handle_t *handle = NULL;
> - loff_t range_start = 0;
> + long pages_written = 0;
> struct mpage_da_data mpd;
> struct inode *inode = mapping->host;
> + int no_nrwrite_update, no_index_update;
> int needed_blocks, ret = 0, nr_to_writebump = 0;
> - long to_write, pages_skipped = 0;
> struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb);
>
> /*
> @@ -2385,23 +2394,27 @@ static int ext4_da_writepages(struct address_space *mapping,
> nr_to_writebump = sbi->s_mb_stream_request - wbc->nr_to_write;
> wbc->nr_to_write = sbi->s_mb_stream_request;
> }
> + if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
> + range_whole = 1;
>
> - if (!wbc->range_cyclic)
> - /*
> - * If range_cyclic is not set force range_cont
> - * and save the old writeback_index
> - */
> - wbc->range_cont = 1;
> -
> - range_start = wbc->range_start;
> - pages_skipped = wbc->pages_skipped;
> + if (wbc->range_cyclic)
> + index = mapping->writeback_index;
> + else
> + index = wbc->range_start >> PAGE_CACHE_SHIFT;
>
> mpd.wbc = wbc;
> mpd.inode = mapping->host;
>
> -restart_loop:
> - to_write = wbc->nr_to_write;
> - while (!ret && to_write > 0) {
> + /*
> + * we don't want write_cache_pages to update
> + * nr_to_write and writeback_index
> + */
> + no_nrwrite_update = wbc->no_nrwrite_update;
> + wbc->no_nrwrite_update = 1;
> + no_index_update = wbc->no_index_update;
> + wbc->no_index_update = 1;
> +
> + while (!ret && wbc->nr_to_write > 0) {
>
> /*
> * we insert one extent at a time. So we need
> @@ -2422,48 +2435,49 @@ static int ext4_da_writepages(struct address_space *mapping,
> dump_stack();
> goto out_writepages;
> }
> - to_write -= wbc->nr_to_write;
> -
> mpd.get_block = ext4_da_get_block_write;
> ret = mpage_da_writepages(mapping, wbc, &mpd);
>
> ext4_journal_stop(handle);
>
> - if (mpd.retval == -ENOSPC)
> + if (mpd.retval == -ENOSPC) {
> + /* commit the transaction which would
> + * free blocks released in the transaction
> + * and try again
> + */
> jbd2_journal_force_commit_nested(sbi->s_journal);
> -
> - /* reset the retry count */
> - if (ret == MPAGE_DA_EXTENT_TAIL) {
> + ret = 0;
> + } else if (ret == MPAGE_DA_EXTENT_TAIL) {
> /*
> * got one extent now try with
> * rest of the pages
> */
> - to_write += wbc->nr_to_write;
> + pages_written += mpd.pages_written;
> ret = 0;
> - } else if (wbc->nr_to_write) {
> + } else if (wbc->nr_to_write)
> /*
> * There is no more writeout needed
> * or we requested for a noblocking writeout
> * and we found the device congested
> */
> - to_write += wbc->nr_to_write;
> break;
> - }
> - wbc->nr_to_write = to_write;
> }
>
> - if (wbc->range_cont && (pages_skipped != wbc->pages_skipped)) {
> - /* We skipped pages in this loop */
> - wbc->range_start = range_start;
> - wbc->nr_to_write = to_write +
> - wbc->pages_skipped - pages_skipped;
> - wbc->pages_skipped = pages_skipped;
> - goto restart_loop;
> - }
> + /* Update index */
> + index += pages_written;
> + if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
> + /*
> + * set the writeback_index so that range_cyclic
> + * mode will write it back later
> + */
> + mapping->writeback_index = index;
>
> out_writepages:
> - wbc->nr_to_write = to_write - nr_to_writebump;
> - wbc->range_start = range_start;
> + if (!no_nrwrite_update)
> + wbc->no_nrwrite_update = 0;
> + if (!no_index_update)
> + wbc->no_index_update = 0;
> + wbc->nr_to_write -= nr_to_writebump;
> return ret;
> }
>
> diff --git a/include/linux/writeback.h b/include/linux/writeback.h
> index 12b15c5..b04287e 100644
> --- a/include/linux/writeback.h
> +++ b/include/linux/writeback.h
> @@ -63,7 +63,10 @@ struct writeback_control {
> unsigned for_writepages:1; /* This is a writepages() call */
> unsigned range_cyclic:1; /* range_start is cyclic */
> unsigned more_io:1; /* more io to be dispatched */
> - unsigned range_cont:1;
> +
> + /* write_cache_pages() control */
> + unsigned no_nrwrite_update:1; /* don't update nr_to_write */
> + unsigned no_index_update:1; /* don't update writeback_index */
> };
>
> /*
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 24de8b6..a85930c 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -876,6 +876,7 @@ int write_cache_pages(struct address_space *mapping,
> pgoff_t end; /* Inclusive */
> int scanned = 0;
> int range_whole = 0;
> + long nr_to_write = wbc->nr_to_write;
>
> if (wbc->nonblocking && bdi_write_congested(bdi)) {
> wbc->encountered_congestion = 1;
> @@ -939,7 +940,7 @@ int write_cache_pages(struct address_space *mapping,
> unlock_page(page);
> ret = 0;
> }
> - if (ret || (--(wbc->nr_to_write) <= 0))
> + if (ret || (--nr_to_write <= 0))
> done = 1;
> if (wbc->nonblocking && bdi_write_congested(bdi)) {
> wbc->encountered_congestion = 1;
> @@ -958,11 +959,13 @@ int write_cache_pages(struct address_space *mapping,
> index = 0;
> goto retry;
> }
> - if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
> + if (!wbc->no_index_update &&
> + (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))) {
> mapping->writeback_index = index;
> + }
> + if (!wbc->no_nrwrite_update)
> + wbc->nr_to_write = nr_to_write;
>
> - if (wbc->range_cont)
> - wbc->range_start = index << PAGE_CACHE_SHIFT;
> return ret;
> }
> EXPORT_SYMBOL(write_cache_pages);
> --
> 1.6.0.1.285.g1070
--
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