Messages in this thread | | | Subject | Re: [v3 PATCH 2/4] mm: move mem_cgroup_uncharge out of __page_cache_release() | From | Yang Shi <> | Date | Thu, 13 Jun 2019 10:13:19 -0700 |
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On 6/13/19 4:39 AM, Kirill A. Shutemov wrote: > On Thu, Jun 13, 2019 at 05:56:47AM +0800, Yang Shi wrote: >> The later patch would make THP deferred split shrinker memcg aware, but >> it needs page->mem_cgroup information in THP destructor, which is called >> after mem_cgroup_uncharge() now. >> >> So, move mem_cgroup_uncharge() from __page_cache_release() to compound >> page destructor, which is called by both THP and other compound pages >> except HugeTLB. And call it in __put_single_page() for single order >> page. > > If I read the patch correctly, it will change behaviour for pages with > NULL_COMPOUND_DTOR. Have you considered it? Are you sure it will not break > anything?
So far a quick search shows NULL_COMPOUND_DTOR is not used by any type of compound page. The HugeTLB code sets destructor to NULL_COMPOUND_DTOR when freeing hugetlb pages via hugetlb specific destructor.
The prep_new_page() would call prep_compound_page() if __GFP_COMP is used, which sets dtor to COMPOUND_PAGE_DTOR by default. Just hugetlb and THP set their specific dtors.
And, it looks __put_compound_page() doesn't check if dtor is NULL or not at all.
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