Re: [PATCH V5 2/8] fs/ceph: vfs __set_page_dirty_nobuffers interface instead of doing it inside filesystem

On Thu, 1 Aug 2013, Yan, Zheng wrote:

On Thu, Aug 1, 2013 at 7:51 PM, Sha Zhengju [off-list ref] wrote:

quoted

From: Sha Zhengju <redacted>

Following we will begin to add memcg dirty page accounting around

__set_page_dirty_

quoted

{buffers,nobuffers} in vfs layer, so we'd better use vfs interface to

avoid exporting

quoted

those details to filesystems.

Signed-off-by: Sha Zhengju <redacted>
---
 fs/ceph/addr.c |   13 +------------
 1 file changed, 1 insertion(+), 12 deletions(-)

diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index 3e68ac1..1445bf1 100644
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c

@@ -76,7 +76,7 @@ static int ceph_set_page_dirty(struct page *page)

        if (unlikely(!mapping))
                return !TestSetPageDirty(page);

-       if (TestSetPageDirty(page)) {
+       if (!__set_page_dirty_nobuffers(page)) {

it's too early to set the radix tree tag here. We should set page's snapshot
context and increase the i_wrbuffer_ref first. This is because once the tag
is set, writeback thread can find and start flushing the page.

Unfortunately I only remember being frustrated by this code.  :)  Looking 
at it now, though, it seems like the minimum fix is to set the 
page->private before marking the page dirty.  I don't know the locking 
rules around that, though.  If that is potentially racy, maybe the safest 
thing would be if __set_page_dirty_nobuffers() took a void* to set 
page->private to atomically while holding the tree_lock.

sage

quoted

                dout("%p set_page_dirty %p idx %lu -- already dirty\n",
                     mapping->host, page, page->index);
                return 0;

@@ -107,14 +107,7 @@ static int ceph_set_page_dirty(struct page *page)

             snapc, snapc->seq, snapc->num_snaps);
        spin_unlock(&ci->i_ceph_lock);

-       /* now adjust page */
-       spin_lock_irq(&mapping->tree_lock);
        if (page->mapping) {    /* Race with truncate? */
-               WARN_ON_ONCE(!PageUptodate(page));
-               account_page_dirtied(page, page->mapping);
-               radix_tree_tag_set(&mapping->page_tree,
-                               page_index(page), PAGECACHE_TAG_DIRTY);
-

this code was coped from __set_page_dirty_nobuffers(). I think the reason
Sage did this is to handle the race described in
__set_page_dirty_nobuffers()'s comment. But I'm wonder if "page->mapping ==
NULL" can still happen here. Because truncate_inode_page() unmap page from
processes's address spaces first, then delete page from page cache.

Regards
Yan, Zheng

quoted

                /*
                 * Reference snap context in page->private.  Also set
                 * PagePrivate so that we get invalidatepage callback.

@@ -126,14 +119,10 @@ static int ceph_set_page_dirty(struct page *page)

                undo = 1;
        }

-       spin_unlock_irq(&mapping->tree_lock);

quoted

-
        if (undo)
                /* whoops, we failed to dirty the page */
                ceph_put_wrbuffer_cap_refs(ci, 1, snapc);

-       __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
-
        BUG_ON(!PageDirty(page));
        return 1;
 }
--
1.7.9.5

--
To unsubscribe from this list: send the line "unsubscribe ceph-devel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html