linux-kernel - Re: [PATCH 6/9] mm/memory: split non-tlb flushing part from zap_page_range

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Message-ID: <bybnnqb4fyr4odgwa5qcgcysgjqjsilptreljgamt7ocb5ue7k@s3lvdf52csbk>
Date: Tue, 1 Apr 2025 10:03:17 -0400
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: SeongJae Park <sj@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        "Liam R. Howlett" <howlett@...il.com>,
        David Hildenbrand <david@...hat.com>,
        Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
        Shakeel Butt <shakeel.butt@...ux.dev>,
        Vlastimil Babka <vbabka@...e.cz>, kernel-team@...a.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 6/9] mm/memory: split non-tlb flushing part from
 zap_page_range_single()

* SeongJae Park <sj@...nel.org> [250331 22:48]:
> On Mon, 31 Mar 2025 21:45:40 -0400 "Liam R. Howlett" <Liam.Howlett@...cle.com> wrote:
> 
> > * SeongJae Park <sj@...nel.org> [250310 13:24]:
> > > Some of zap_page_range_single() callers such as [process_]madvise() with
> > > MADV_DONEED[_LOCKED] cannot batch tlb flushes because
> > > zap_page_range_single() does tlb flushing for each invocation.  Split
> > > out the body of zap_page_range_single() except mmu_gather object
> > > initialization and gathered tlb entries flushing parts for such batched
> > > tlb flushing usage.
> > > 
> > > Signed-off-by: SeongJae Park <sj@...nel.org>
> > > ---
> > >  mm/memory.c | 36 ++++++++++++++++++++++--------------
> > >  1 file changed, 22 insertions(+), 14 deletions(-)
> > > 
> > > diff --git a/mm/memory.c b/mm/memory.c
> > > index 78c7ee62795e..88c478e2ed1a 100644
> > > --- a/mm/memory.c
> > > +++ b/mm/memory.c
> > > @@ -1995,38 +1995,46 @@ void unmap_vmas(struct mmu_gather *tlb, struct ma_state *mas,
> > >  	mmu_notifier_invalidate_range_end(&range);
> > >  }
> > >  
> > > -/**
> > > - * zap_page_range_single - remove user pages in a given range
> > > - * @vma: vm_area_struct holding the applicable pages
> > > - * @address: starting address of pages to zap
> > > - * @size: number of bytes to zap
> > > - * @details: details of shared cache invalidation
> > > - *
> > > - * The range must fit into one VMA.
> > > - */
> > > -void zap_page_range_single(struct vm_area_struct *vma, unsigned long address,
> > > +static void unmap_vma_single(struct mmu_gather *tlb,
> > 
> > I could not, for the life of me, figure out what was going on here until
> > I realised that is is a new function name and not unmap_single_vma(),
> > which is called below.
> 
> Agreed, definitely the name is confusing, especially given the existence of
> unmap_single_vma().
> 
> > 
> > Can we name this differently somehow?  notify_unmap_single_vma() or
> > something better?
> 
> notify_unmap_single_vma() sounds good to me.  I'll use the name in the next
> revision unless we find a better one.

Thanks.  I don't really mind if you have anything else to name it, as
long as it reduces the confusion.

> 
> > 
> > Also, maybe add a description of the function to this patch vs the next
> > patch?
> 
> That makes sense.  In the next revision, I will add the kernel-doc comment
> here, but not as a valid kernel-doc comment (maybe wtarts with /* instead of
> /**) since this function is a static function as of this patch.  On the next
> patch that makes this non-static, I will make the comment a valid kernel-doc
> comment with a minimum change.
> 
> I prefer not having a valid kernel-doc comment for static function, but that's
> just a personal preferrence and I have no strong reason to object other way.
> Please feel free to let me know if you prefer making it valid kernel doc
> comment starting from this patch.
> 

Yes, that was what I was thinking as well.

...

Thanks,
Liam