linux-kernel - Re: [RFC PATCH] mm: remove zap_page_range and change callers to use zap_vma_page

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Date:   Mon, 19 Dec 2022 11:22:47 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Michal Hocko <mhocko@...e.com>,
        Jérôme Glisse <jglisse@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
        linux-s390@...r.kernel.org, netdev@...r.kernel.org,
        David Hildenbrand <david@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Rik van Riel <riel@...riel.com>,
        Will Deacon <will@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Palmer Dabbelt <palmer@...belt.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Christian Brauner <brauner@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH] mm: remove zap_page_range and change callers to use
 zap_vma_page_range

On 12/19/22 13:06, Michal Hocko wrote:
> On Fri 16-12-22 11:20:12, Mike Kravetz wrote:
> > zap_page_range was originally designed to unmap pages within an address
> > range that could span multiple vmas.  While working on [1], it was
> > discovered that all callers of zap_page_range pass a range entirely within
> > a single vma.  In addition, the mmu notification call within zap_page
> > range does not correctly handle ranges that span multiple vmas as calls
> > should be vma specific.
> 
> Could you spend a sentence or two explaining what is wrong here?

Hmmmm?  My assumption was that the range passed to mmu_notifier_range_init()
was supposed to be within the specified vma.  When looking into the notifier
routines, I could not find any documentation about the usage of the vma within
the mmu_notifier_range structure.  It was introduced with commit bf198b2b34bf
"mm/mmu_notifier: pass down vma and reasons why mmu notifier is happening".
However, I do not see this being used today.

Of course, I could be missing something, so adding Jérôme.

> 
> > Instead of fixing zap_page_range, change all callers to use the new
> > routine zap_vma_page_range.  zap_vma_page_range is just a wrapper around
> > zap_page_range_single passing in NULL zap details.  The name is also
> > more in line with other exported routines that operate within a vma.
> > We can then remove zap_page_range.
> 
> I would stick with zap_page_range_single rather than adding a new
> wrapper but nothing really critical.

I am fine with doing that as well.  My only reason for the wrapper is that all 
callers outside mm/memory.c would pass in NULL zap details.

> 
> > Also, change madvise_dontneed_single_vma to use this new routine.
> > 
> > [1] https://lore.kernel.org/linux-mm/20221114235507.294320-2-mike.kravetz@oracle.com/
> > Suggested-by: Peter Xu <peterx@...hat.com>
> > Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
> 
> Other than that LGTM
> Acked-by: Michal Hocko <mhocko@...e.com>
> 
> Thanks!

Thanks for taking a look.
-- 
Mike Kravetz