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

On Fri, Aug 2, 2013 at 2:27 AM, Sage Weil [off-list ref] wrote:

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

quoted

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.

Sorry, I don't catch the point of your last sentence... Could you
please explain it again?

I notice there is a check in __set_page_dirty_nobuffers():
      WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
So does it mean we can only set page->private after it? but if so the
__mark_inode_dirty is still ahead of setting snapc.


Thanks,
Sha

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