linux-kernel - Re: [PATCH] mm: reuse the unshared swapcache page in do_wp

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Date:   Thu, 20 Jan 2022 19:19:51 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Nadav Amit <nadav.amit@...il.com>
Cc:     "zhangliang (AG)" <zhangliang5@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        wangzhigang17@...wei.com, Matthew Wilcox <willy@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] mm: reuse the unshared swapcache page in do_wp_page

>> Sounds good? At least to me. If only swap/migration entries wouldn't be
>> harder to handle than I'd wish, that's why it's taking a little and will
>> take a little longer.
> 
> Thanks for the quick response. I would have to see the logic to set/clear
> PageAnonExclusive to fully understand how things are handled.
> 

I'll let you know as soon as I have something. I'll most probably share
a document explaining the design first.

> BTW, I just saw this patch form PeterZ [1] that seems to be related, as
> it deals with changing protection on pinned pages.

Unfortunately the use of page_maybe_dma_pinned() is racy, as we can race
with GUP fast. It's a problem for vmscan which currently relies on it
for correctness. For migration, it might be good enough as we should
fail later when trying to freeze the refcount.

> 
> 
> [1] https://lore.kernel.org/linux-mm/20220120160822.666778608@infradead.org/
> 


-- 
Thanks,

David / dhildenb