Re: [RFC PATCH v3 03/12] mm: memcontrol: make lruvec lock safe when the LRU pages reparented
From: Roman Gushchin
Date: Tue May 25 2021 - 13:22:16 EST
On Wed, Apr 21, 2021 at 03:00:50PM +0800, Muchun Song wrote:
> The diagram below shows how to make the page lruvec lock safe when the
> LRU pages reparented.
> lruvec = mem_cgroup_page_lruvec(page);
> // The page is reparented at this time.
> if (unlikely(lruvec_memcg(lruvec) != page_memcg(page)))
> // Acquired the wrong lruvec lock and need to retry.
> // Because this page is on the parent memcg lruvec list.
> goto retry;
> // If we reach here, it means that page_memcg(page) is stable.
> // lruvec belongs to memcg and lruvec_parent belongs to parent memcg.
> // Move all the pages from the lruvec list to the parent lruvec list.
> After we acquire the lruvec lock, we need to check whether the page is
> reparented. If so, we need to reacquire the new lruvec lock. On the
> routine of the LRU pages reparenting, we will also acquire the lruvec
> lock (Will be implemented in the later patch). So page_memcg() cannot
> be changed when we hold the lruvec lock.
> Since lruvec_memcg(lruvec) is always equal to page_memcg(page) after
> we hold the lruvec lock, lruvec_memcg_debug() check is pointless. So
> remove it.
> This is a preparation for reparenting the LRU pages.
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Acked-by: Roman Gushchin <guro@xxxxxx>