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ext4: Use our own write_cache_pages() 

Make a copy of write_cache_pages() for the benefit of
ext4_da_writepages().  This allows us to simplify the code some, and
will allow us to further customize the code in future patches.

There are some nasty hacks in write_cache_pages(), which Linus has
(correctly) characterized as vile.  I've just copied it into
write_cache_pages_da(), without trying to clean those bits up lest I
break something in the ext4's delalloc implementation, which is a bit
fragile right now.  This will allow Dave Chinner to clean up
write_cache_pages() in mm/page-writeback.c, without worrying about
breaking ext4.  Eventually write_cache_pages_da() will go away when I
rewrite ext4's delayed allocation and create a general
ext4_writepages() which is used for all of ext4's writeback.  Until
now this is the lowest risk way to clean up the core
write_cache_pages() function.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: Dave Chinner <david@fromorbit.com>
This commit is contained in:
Theodore Ts'o 2010-05-16 18:00:00 -04:00
parent 39a4bade8c
commit 8e48dcfbd7
1 changed files with 119 additions and 22 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

141
fs/ext4/inode.c
View File

@ -2426,17 +2426,6 @@ static int __mpage_da_writepage(struct page *page,
struct buffer_head *bh, *head;
sector_t logical;
if (mpd->io_done) {
/*
* Rest of the page in the page_vec
* redirty then and skip then. We will
* try to write them again after
* starting a new transaction
*/
redirty_page_for_writepage(wbc, page);
unlock_page(page);
return MPAGE_DA_EXTENT_TAIL;
}
/*
* Can we merge this page to current extent?
*/
@ -2831,6 +2820,124 @@ static int ext4_da_writepages_trans_blocks(struct inode *inode)
return ext4_chunk_trans_blocks(inode, max_blocks);
}
/*
* 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
*/
static int write_cache_pages_da(struct address_space *mapping,
struct writeback_control *wbc,
struct mpage_da_data *mpd)
{
int ret = 0;
int done = 0;
struct pagevec pvec;
int nr_pages;
pgoff_t index;
pgoff_t end; /* Inclusive */
long nr_to_write = wbc->nr_to_write;
pagevec_init(&pvec, 0);
index = wbc->range_start >> PAGE_CACHE_SHIFT;
end = wbc->range_end >> PAGE_CACHE_SHIFT;
while (!done && (index <= end)) {
int i;
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];
/*
* At this point, the page may be truncated or
* invalidated (changing page->mapping to NULL), or
* even swizzled back from swapper_space to tmpfs file
* mapping. However, page->index will not change
* because we have a reference on the page.
*/
if (page->index > end) {
done = 1;
break;
}
lock_page(page);
/*
* Page truncated or invalidated. We can freely skip it
* then, even for data integrity operations: the page
* has disappeared concurrently, so there could be no
* real expectation of this data interity operation
* even if there is now a new, dirty page at the same
* pagecache address.
*/
if (unlikely(page->mapping != mapping)) {
continue_unlock:
unlock_page(page);
continue;
}
if (!PageDirty(page)) {
/* someone wrote it for us */
goto continue_unlock;
}
if (PageWriteback(page)) {
if (wbc->sync_mode != WB_SYNC_NONE)
wait_on_page_writeback(page);
else
goto continue_unlock;
}
BUG_ON(PageWriteback(page));
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) {
unlock_page(page);
ret = 0;
} else {
done = 1;
break;
}
}
if (nr_to_write > 0) {
nr_to_write--;
if (nr_to_write == 0 &&
wbc->sync_mode == WB_SYNC_NONE) {
/*
* We stop writing back only if we are
* not doing integrity sync. In case of
* integrity sync we have to keep going
* because someone may be concurrently
* dirtying pages, and we might have
* synced a lot of newly appeared dirty
* pages, but have not synced all of the
* old dirty pages.
*/
done = 1;
break;
}
}
}
pagevec_release(&pvec);
cond_resched();
}
return ret;
}
static int ext4_da_writepages(struct address_space *mapping,
struct writeback_control *wbc)
{
@ -2839,7 +2946,6 @@ static int ext4_da_writepages(struct address_space *mapping,
handle_t *handle = NULL;
struct mpage_da_data mpd;
struct inode *inode = mapping->host;
int no_nrwrite_index_update;
int pages_written = 0;
long pages_skipped;
unsigned int max_pages;
@ -2919,12 +3025,6 @@ static int ext4_da_writepages(struct address_space *mapping,
mpd.wbc = wbc;
mpd.inode = mapping->host;
/*
* we don't want write_cache_pages to update
* nr_to_write and writeback_index
*/
no_nrwrite_index_update = wbc->no_nrwrite_index_update;
wbc->no_nrwrite_index_update = 1;
pages_skipped = wbc->pages_skipped;
retry:
@ -2966,8 +3066,7 @@ retry:
mpd.io_done = 0;
mpd.pages_written = 0;
mpd.retval = 0;
ret = write_cache_pages(mapping, wbc, __mpage_da_writepage,
&mpd);
ret = write_cache_pages_da(mapping, wbc, &mpd);
/*
* If we have a contiguous extent of pages and we
* haven't done the I/O yet, map the blocks and submit
@ -3033,8 +3132,6 @@ retry:
mapping->writeback_index = index;
out_writepages:
if (!no_nrwrite_index_update)
wbc->no_nrwrite_index_update = 0;
wbc->nr_to_write -= nr_to_writebump;
wbc->range_start = range_start;
trace_ext4_da_writepages_result(inode, wbc, ret, pages_written);