linux-kernel - Re: Ack to merge through DRM? WAS Re: [PATCH v2 1/5] mm: Add write-protect and clean utilities for address space ranges

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Date:   Mon, 30 Sep 2019 19:38:31 +0200
From:   Thomas Hellström (VMware) 
        <thomas_os@...pmail.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux-MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: Ack to merge through DRM? WAS Re: [PATCH v2 1/5] mm: Add
 write-protect and clean utilities for address space ranges

On 9/30/19 7:12 PM, Linus Torvalds wrote:
> On Mon, Sep 30, 2019 at 6:04 AM Kirill A. Shutemov <kirill@...temov.name> wrote:
>> Have you seen page_vma_mapped_walk()? I made it specifically for rmap code
>> to cover cases when a THP is mapped with PTEs. To me it's not a big
>> stretch to make it cover multiple pages too.
> I agree that is closer, but it does make for calling that big complex
> function for every iteration step.
>
> Of course, you are right that the callback approach is problematic
> too, now that we have retpoline issues, making those very expensive.
> But at least that hopefully gets fixed some day and gets to be a rare
> problem.
>
> Matter ot taste, I guess.
>
>                Linus

Matthew Wilcox suggested something similar before the pagewalk.c rewrite:

https://lore.kernel.org/lkml/20190806190937.GD30179@bombadil.infradead.org/

Still, In this case I'd opt for using the pagewalk code: In the dirty 
helpers we don't ever use a struct page, but only deal with PTE entries, 
same as the pagewalk code does, but not page_vma_mapped_walk(). The 
underlying memory may well be IO memory.

/Thomas