On Fri, Aug 2, 2013 at 5:04 PM, Sha Zhengju [off-list ref] wrote:

On Thu, Aug 1, 2013 at 11:19 PM, Yan, Zheng [off-list ref] 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_
{buffers,nobuffers} in vfs layer, so we'd better use vfs interface to
avoid exporting
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.

OK, thanks for pointing it out.

quoted

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.

But in non-mmap case, doesn't it has no relation to 'unmap page from
address spaces'?

In non-mmap case, page is locked when the set_page_dirty() callback is called.
truncate_inode_page() waits until the page is unlocked, then delete it from the
page cache.

Regards
Yan, Zheng

The check is exactly avoiding racy with delete_from_page_cache(),
since the two both need to hold mapping->tree_lock, and if truncate
goes first then __set_page_dirty_nobuffers() may have NULL mapping.


Thanks,
Sha

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