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 16:03:57 +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 Fri, Sep 27, 2019 at 09:39:48AM -0700, Linus Torvalds wrote:
> On Fri, Sep 27, 2019 at 5:17 AM Kirill A. Shutemov <kirill@...temov.name> wrote:
> >
> > > 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.
> 
> Well, that's very questionable.
> 
> The rmap code mainly does the "page -> virtual" mapping.  One page at a time.
> 
> The page walker code does the "virtual -> pte" mapping. Always a whole
> range at a time.

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.

> So I think conceptually, mm/memory.c and unmap_mapping_range() is
> closest but I don't think it's practical to share code.
> 
> And between mm/pagewalk.c and mm/rmap.c, I think the page walking has
> way more of actual practical code sharing, and is also conceptually
> closer because most of the code is about walking a range, not looking
> up the mapping of one page.

I guess it's matter of personal preferences, but page table walkers based
on callback always felt wrong to me.

-- 
 Kirill A. Shutemov