On Thu, Aug 1, 2013 at 11:19 PM, Yan, Zheng <ukernel@xxxxxxxxx> wrote:
> On Thu, Aug 1, 2013 at 7:51 PM, Sha Zhengju <handai.szj@xxxxxxxxx> wrote:
>> From: Sha Zhengju <handai.szj@xxxxxxxxxx>
>>
>> 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 <handai.szj@xxxxxxxxxx>
>> ---
>> 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.
>
>
>> 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'?
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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