On Wed, Oct 07, 2009 at 09:29:24PM +0800, Wu Fengguang wrote:
> On Wed, Oct 07, 2009 at 07:37:35PM +0800, Nikita Danilov wrote:
> > 2009/10/7 Wu Fengguang <fengguang.wu@xxxxxxxxx>:
> > > On Wed, Oct 07, 2009 at 06:38:37PM +0800, Nikita Danilov wrote:
> > >> Hello,
> > >>
> >
> > [...]
> >
> > >
> > > Glad to know about your experiences :) Interestingly I started with
> > > ->writepage() and then switch to ->writepages() because filesystems
> > > behave better with the latter (i.e. less file fragmentation).
> >
> > By the way, why is your patch doing
> >
> > ->writepage(page->index);
> > generic_writepages(page->index + 1, LUMPY_PAGEOUT_PAGES - 1);
> >
> > instead of
> >
> > generic_writepages(page->index, LUMPY_PAGEOUT_PAGES);
> >
> > ? Is this because of the difficulties with passing back page specific
> > errors from generic_writepages()?
>
> Yes. It's possible to tell write_cache_pages() to return
> AOP_WRITEPAGE_ACTIVATE. Other ->writepages() don't have to deal with
> this because their ->writepage() won't return AOP_WRITEPAGE_ACTIVATE
> at all.
>
> But it is going to be ugly to specialize the first locked page in
> every ->writepages() functions..
>
> > >
> > > I'd like to just ignore the shmem case, by adding a
> > > bdi_cap_writeback_dirty() check. Because clustered writing to swap
> > > device may be a less gain.
> >
> > Or you can just call try_to_unmap() from shmem_writepage() when
> > wbc->for_reclaim is true.
>
> Hmm, it's more comfortable to stay away from shmem for the initial version.
> But feel free to submit a patch for it in future :)
>
> > > Page filtering should also be possible in write_cache_pages(). But
> > > what do you mean by "hard-to-fix races against inode reclamation"?
> >
> > vmscan.c pageout path doesn't take a reference on inode, so the
> > instant ->writepage() releases lock on the page, the inode can be
> > freed.
>
> Ah, then we could just do igrab() if inode_lock is not locked?
> A bit ugly though.
Since writepage() can sleep, we don't need to worry about inode_lock.
Here is the updated patch.
Thanks,
Fengguang
---
vmscan: lumpy pageout
When pageout a dirty page, try to piggy back more consecutive dirty
pages (up to 512KB) to improve IO efficiency.
Only ext3/reiserfs which don't have its own aops->writepages are
supported in this initial version.
CC: Dave Chinner <david@xxxxxxxxxxxxx>
CC: Nikita Danilov <danilov@xxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
mm/page-writeback.c | 12 ++++++++++++
mm/vmscan.c | 16 ++++++++++++++++
2 files changed, 28 insertions(+)
--- linux.orig/mm/vmscan.c 2009-10-07 21:39:13.000000000 +0800
+++ linux/mm/vmscan.c 2009-10-07 21:39:57.000000000 +0800
@@ -344,6 +344,8 @@ typedef enum {
PAGE_CLEAN,
} pageout_t;
+#define LUMPY_PAGEOUT_PAGES (512 * 1024 / PAGE_CACHE_SIZE)
+
/*
* pageout is called by shrink_page_list() for each dirty page.
* Calls ->writepage().
@@ -399,16 +401,30 @@ static pageout_t pageout(struct page *pa
.for_reclaim = 1,
};
+ igrab(mapping->host);
SetPageReclaim(page);
res = mapping->a_ops->writepage(page, &wbc);
if (res < 0)
handle_write_error(mapping, page, res);
if (res == AOP_WRITEPAGE_ACTIVATE) {
ClearPageReclaim(page);
+ iput(mapping->host);
return PAGE_ACTIVATE;
}
/*
+ * only write_cache_pages() supports for_reclaim for now
+ * ignore shmem for now, thanks to Nikita.
+ */
+ if (bdi_cap_writeback_dirty(mapping->backing_dev_info) &&
+ !mapping->a_ops->writepages) {
+ wbc.range_start = (page->index + 1) << PAGE_CACHE_SHIFT;
+ wbc.nr_to_write = LUMPY_PAGEOUT_PAGES - 1;
+ generic_writepages(mapping, &wbc);
+ iput(mapping->host);
+ }
+
+ /*
* Wait on writeback if requested to. This happens when
* direct reclaiming a large contiguous area and the
* first attempt to free a range of pages fails.
--- linux.orig/mm/page-writeback.c 2009-10-07 21:39:13.000000000 +0800
+++ linux/mm/page-writeback.c 2009-10-07 21:39:14.000000000 +0800
@@ -805,6 +805,11 @@ int write_cache_pages(struct address_spa
break;
}
+ if (wbc->for_reclaim && done_index != page->index) {
+ done = 1;
+ break;
+ }
+
if (nr_to_write != wbc->nr_to_write &&
done_index + WB_SEGMENT_DIST < page->index &&
--wbc->nr_segments <= 0) {
@@ -846,6 +851,13 @@ continue_unlock:
if (!clear_page_dirty_for_io(page))
goto continue_unlock;
+ /*
+ * active and unevictable pages will be checked at
+ * rotate time
+ */
+ if (wbc->for_reclaim)
+ SetPageReclaim(page);
+
ret = (*writepage)(page, wbc, data);
if (unlikely(ret)) {
if (ret == AOP_WRITEPAGE_ACTIVATE) {
--
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