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To:     "zhangliang (AG)" <zhangliang5@huawei.com>
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From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Subject: Re: [PATCH] mm: reuse the unshared swapcache page in do_wp_page
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On 17.01.22 14:31, zhangliang (AG) wrote:
> Sure, I will do that :)

I'm polishing up / testing the patches and might send something out for discussion shortly.
Just a note that on my branch was a version with a wrong condition that should have been fixed now.

I am still thinking about PTE mapped THP. For these, we'll always
have page_count() > 1, essentially corresponding to the number of still-mapped sub-pages.

So if we end up with a R/O mapped part of a THP, we'll always have to COW and cannot reuse ever,
although it's really just a single process mapping the THP via PTEs.

One approach would be to scan the currently locked page table for entries mapping
this same page. If page_count() corresponds to that value, we know that only we are
mapping the THP and there are no additional references. That would be a special case
if we find an anon THP in do_wp_page(). Hm.

-- 
Thanks,

David / dhildenb