linux-kernel - Re: [PATCH 0/9] mm/madvise: batch tlb flushes for MADV_DONTNEED and MADV

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Message-ID: <a4fa3cd2-ba8e-4d23-a513-e3f54456306c@lucifer.local>
Date: Tue, 11 Mar 2025 11:17:51 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Roman Gushchin <roman.gushchin@...ux.dev>
Cc: Shakeel Butt <shakeel.butt@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        SeongJae Park <sj@...nel.org>, "Liam R. Howlett" <howlett@...il.com>,
        David Hildenbrand <david@...hat.com>, Vlastimil Babka <vbabka@...e.cz>,
        kernel-team@...a.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 0/9] mm/madvise: batch tlb flushes for MADV_DONTNEED and
 MADV_FREE

On Mon, Mar 10, 2025 at 11:36:52PM +0000, Roman Gushchin wrote:
> On Mon, Mar 10, 2025 at 04:15:06PM -0700, Shakeel Butt wrote:
> > On Mon, Mar 10, 2025 at 03:39:21PM -0700, Andrew Morton wrote:
> > > On Mon, 10 Mar 2025 10:23:09 -0700 SeongJae Park <sj@...nel.org> wrote:
> > >
> > > >  It is unclear if such use case
> > > > is common and the inefficiency is significant.
> > >
> > > Well, we could conduct a survey,
> > >
> > > Can you add some logging to detect when userspace performs such an
> > > madvise() call, then run that kernel on some "typical" machines which
> > > are running "typical" workloads?  That should give us a feeling for how
> > > often userspace does this, and hence will help us understand the usefulness
> > > of this patchset.
> >
> > Just for the clarification, this patchset is very useful for the
> > process_madvise() and the experiment results show that.
>
> +1
>
> Google carried an internal version for a vectorized madvise() which
> was much faster than process_madvise() last time I measured it.
> I hope SJ's patchset will (partially) address this difference,
> which will hopefully allow to drop the internal implementation
> for process_madvise.

Relatedly I also feel, at some point, we ought to remove the UIO_FASTIOV
limit on process_madvise().

But one for a future series...