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Date: Fri, 10 Oct 2008 23:44:43 +0530
From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To: cmm@...ibm.com, tytso@....edu, sandeen@...hat.com
Cc: linux-ext4@...r.kernel.org,
"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: [PATCH -V3] ext4: Fix file fragmentation during large file write.
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.
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..4f359f4 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 && 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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