On Thu, Jan 7, 2021 at 4:39 PM Michal Hocko [off-list ref] wrote:

On Thu 07-01-21 11:11:41, Muchun Song wrote:

quoted

On Thu, Jan 7, 2021 at 1:07 AM Michal Hocko [off-list ref] wrote:

quoted

On Wed 06-01-21 16:47:37, Muchun Song wrote:

quoted

When dissolve_free_huge_page() races with __free_huge_page(), we can
do a retry. Because the race window is small.

Is this a bug fix or mere optimization. I have hard time to tell from
the description.

It is optimization. Thanks.

quoted

quoted

Signed-off-by: Muchun Song <redacted>
---
 mm/hugetlb.c | 26 +++++++++++++++++++++-----
 1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c

[...]

quoted

@@ -1825,6 +1828,14 @@ int dissolve_free_huge_page(struct page *page)
      }
 out:
      spin_unlock(&hugetlb_lock);
+
+     /*
+      * If the freeing of the HugeTLB page is put on a work queue, we should
+      * flush the work before retrying.
+      */
+     if (unlikely(rc == -EAGAIN))
+             flush_work(&free_hpage_work);

Is it safe to wait for the work to finish from this context?

Yes. It is safe.

Please expand on why in the changelog. Same for the optimization
including some numbers showing it really helps.

OK. Changelog should be updated. Do you agree the race window
is quite small? If so, why is it not an optimization? Don’t we dissolve
the page as successfully as possible when we call
dissolve_free_huge_page()? I am confused about numbers showing.
Because this is not a performance optimization, but an increase in
the success rate of dissolving.

Thanks.

--
Michal Hocko
SUSE Labs