On Tue, Jan 12, 2021 at 8:37 PM Michal Hocko mhocko@suse.com wrote:
On Tue 12-01-21 19:43:21, Muchun Song wrote:
On Tue, Jan 12, 2021 at 7:17 PM Michal Hocko mhocko@suse.com wrote:
On Tue 12-01-21 18:13:02, Muchun Song wrote:
On Tue, Jan 12, 2021 at 6:02 PM Michal Hocko mhocko@suse.com wrote:
On Sun 10-01-21 20:40:14, Muchun Song wrote: [...]
@@ -1770,6 +1788,14 @@ int dissolve_free_huge_page(struct page *page) int nid = page_to_nid(head); if (h->free_huge_pages - h->resv_huge_pages == 0) goto out;
/** We should make sure that the page is already on the free list* when it is dissolved.*/if (unlikely(!PageHugeFreed(head)))goto out;Do you really want to report EBUSY in this case? This doesn't make much sense to me TBH. I believe you want to return 0 same as when you race and the page is no longer PageHuge.
Return 0 is wrong. Because the page is not freed to the buddy allocator. IIUC, dissolve_free_huge_page returns 0 when the page is already freed to the buddy allocator. Right?
0 is return when the page is either dissolved or it doesn't need dissolving. If there is a race with somebody else freeing the page then there is nothing to dissolve. Under which condition it makes sense to report the failure and/or retry dissolving?
If there is a race with somebody else freeing the page, the page can be freed to the hugepage pool not the buddy allocator. Do you think that this page is dissolved?
OK, I see what you mean. Effectively the page would be in a limbo, not yet in the pool nor in the allocator but it can find its way to the either of the two. But I still dislike returning a failure because that would mean e.g. memory hotplug to fail. Can you simply retry inside this code path (drop the lock, cond_resched and retry)?
Yeah. This is what I want to do (making the memory hotplug as successful as possible). So I send the patch:
[PATCH v3 4/6] mm: hugetlb: add return -EAGAIN for dissolve_free_huge_page
Adding a simple retry inside this function when hitting this race is also fine to me. I can do that.
-- Michal Hocko SUSE Labs