On Sat, Aug 3, 2013 at 4:30 AM, Sage Weil <sage@xxxxxxxxxxx> wrote:
> On Fri, 2 Aug 2013, Sha Zhengju wrote:
>> On Fri, Aug 2, 2013 at 2:27 AM, Sage Weil <sage@xxxxxxxxxxx> wrote:
>> > On Thu, 1 Aug 2013, Yan, Zheng 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.
>> >
>> > 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?
>
> It didn't make much sense. :) I was worried about multiple callers to
> set_page_dirty, but as understand it, this all happens under page->lock,
> right? (There is a mention of other special cases in mm/page-writeback.c,
> but I'm hoping we don't need to worry about that.)
I agree, page lock can handle the concurrent access.
>
> In any case, I suspect what we actually want is something like the below
> (untested) patch. The snapc accounting can be ignored here because
> invalidatepage will clean it up...
>
> sage
>
>
>
> diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
> index afb2fc2..7602e46 100644
> --- a/fs/ceph/addr.c
> +++ b/fs/ceph/addr.c
> @@ -76,9 +76,10 @@ static int ceph_set_page_dirty(struct page *page)
> if (unlikely(!mapping))
> return !TestSetPageDirty(page);
>
> - if (TestSetPageDirty(page)) {
> + if (PageDirty(page)) {
> dout("%p set_page_dirty %p idx %lu -- already dirty\n",
> mapping->host, page, page->index);
> + BUG_ON(!PagePrivate(page));
> return 0;
> }
>
> @@ -107,35 +108,16 @@ 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);
> -
> - /*
> - * Reference snap context in page->private. Also set
> - * PagePrivate so that we get invalidatepage callback.
> - */
> - page->private = (unsigned long)snapc;
> - SetPagePrivate(page);
> - } else {
> - dout("ANON set_page_dirty %p (raced truncate?)\n", page);
> - undo = 1;
> - }
> -
> - spin_unlock_irq(&mapping->tree_lock);
> -
> - 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);
> + /*
> + * Reference snap context in page->private. Also set
> + * PagePrivate so that we get invalidatepage callback.
> + */
> + BUG_ON(PagePrivate(page));
> + page->private = (unsigned long)snapc;
> + SetPagePrivate(page);
>
> - BUG_ON(!PageDirty(page));
> - return 1;
> + return __set_page_dirty_nobuffers(page);
> }
>
> /*
Looks good. Since page lock can avoid multiple access, the undo logic
is also not necessary anymore. Thank you very much!
--
Thanks,
Sha
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