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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Message-ID: <20190927121754.kn46qh2crvsnw5z2@box>
Date:   Fri, 27 Sep 2019 15:17:54 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Thomas Hellström (VMware) 
        <thomas_os@...pmail.org>,
        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 Thu, Sep 26, 2019 at 01:16:55PM -0700, Linus Torvalds wrote:
> On Thu, Sep 26, 2019 at 1:09 PM Thomas Hellström (VMware)
> <thomas_os@...pmail.org> wrote:
> >
> > That said, if people are OK with me modifying the assert in
> > pud_trans_huge_lock() and make __walk_page_range non-static, it should
> > probably be possible to make it work, yes.
> 
> I don't think you need to modify that assert at all.
> 
> That thing only exists when there's a "pud_entry" op in the walker,
> and then you absolutely need to have that mmap_lock.
> 
> As far as I can tell, you fundamentally only ever work on a pte level
> in your address space walker already and actually have a WARN_ON() on
> the pud_huge thing, so no pud entry can possibly apply.
> 
> So no, the assert in pud_trans_huge_lock() does not seem to be a
> reason not to just use the existing page table walkers.
> 
> And once you get rid of the walking, what is left? Just the "iterate
> over the inode mappings" part. Which could just be done in
> mm/pagewalk.c, and then you don't even need to remove the static.
> 
> So making it be just another walking in pagewalk.c would seem to be
> the simplest model.
> 
> Call it "walk_page_mapping()". And talk extensively about how the
> locking differs a lot from the usual "walk_page_vma()" things.

Walking mappings of a page is what rmap does. This code thas to be
integrated there.

-- 
 Kirill A. Shutemov