Re: [PATCH] jfs: clear PAGECACHE_TAG_DIRTY for no-write pages

Dave Kleikamp
2007-12-28T16:53:30Z

On Fri, 2007-12-28 at 10:25 -0600, Dave Kleikamp wrote:
> On Fri, 2007-12-28 at 12:33 +0100, Peter Zijlstra wrote:

> > I'm not liking this open-coded tag_clear, although I currently fail to
> > come up with a nice solution.
>
> I'm looking at __block_write_full_page() for guidance. The situation
> here is similar to writing a page where all the bufferheads are clean.
> __block_write_full_page() always calls set_page_writeback(page), and
> then, if no I/O is initiated, immediately calls
> end_page_writeback(page).
>
> I'll put together a patch for testing.

Here it is, compile-test only so far. I borrowed some of the changeset
comments from Fengguang.

JFS: clear PAGECACHE_TAG_DIRTY for no-write pages

When JFS decides to drop a dirty metapage, it simply clears the META_dirty bit
and leave alone the PG_dirty and PAGECACHE_TAG_DIRTY bits.

When such no-write page goes to metapage_writepage(), the `relic'
PAGECACHE_TAG_DIRTY tag should be cleared, to prevent pdflush from
repeatedly trying to sync them. This is done through
set_page_writeback(), so call it should be called in all cases. If
no I/O is initiated, end_page_writeback() should be called immediately.

This is how __block_write_full_page() does things.

Signed-off-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
CC: Fengguang Wu <wfg@mail.ustc.edu.cn>
---

diff -Nurp linux-2.6.24-rc6-git5/fs/jfs/jfs_metapage.c linux/fs/jfs/jfs_metapage.c
--- linux-2.6.24-rc6-git5/fs/jfs/jfs_metapage.c 2007-12-28 10:28:33.000000000 -0600
+++ linux/fs/jfs/jfs_metapage.c 2007-12-28 10:37:30.000000000 -0600
@@ -360,6 +360,7 @@ static int metapage_writepage(struct pag
struct metapage *mp;
int redirty = 0;
sector_t lblock;
+ int nr_underway = 0;
sector_t pblock;
sector_t next_block = 0;
sector_t page_start;
@@ -371,6 +372,7 @@ static int metapage_writepage(struct pag
(PAGE_CACHE_SHIFT - inode->i_blkbits);
BUG_ON(!PageLocked(page));
BUG_ON(PageWriteback(page));
+ set_page_writeback(page);

for (offset = 0; offset < PAGE_CACHE_SIZE; offset += PSIZE) {
mp = page_to_mp(page, offset);
@@ -413,11 +415,10 @@ static int metapage_writepage(struct pag
if (!bio->bi_size)
goto dump_bio;
submit_bio(WRITE, bio);
+ nr_underway++;
bio = NULL;
- } else {
- set_page_writeback(page);
+ } else
inc_io(page);
- }
xlen = (PAGE_CACHE_SIZE - offset) >> inode->i_blkbits;
pblock = metapage_get_blocks(inode, lblock, &xlen);
if (!pblock) {
@@ -449,12 +450,16 @@ static int metapage_writepage(struct pag
goto dump_bio;

submit_bio(WRITE, bio);
+ nr_underway++;
}
if (redirty)
redirty_page_for_writepage(wbc, page);

unlock_page(page);

+ if (nr_underway == 0)
+ end_page_writeback(page);
+
return 0;
add_failed:
/* We should never reach here, since we're only adding one vec */

--
David Kleikamp
IBM Linux Technology Center