linux-kernel - Re: [PATCH v4 0/5] move per-vma lock into vm_area

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Message-ID: <CAJuCfpHZH5MHVPeV_EgNb8cMR6hqq5p=Y76tgRCZK6mXL4LG=A@mail.gmail.com>
Date: Fri, 22 Nov 2024 07:06:49 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Matthew Wilcox <willy@...radead.org>, Shakeel Butt <shakeel.butt@...ux.dev>, 
	akpm@...ux-foundation.org, liam.howlett@...cle.com, mhocko@...e.com, 
	vbabka@...e.cz, hannes@...xchg.org, mjguzik@...il.com, oliver.sang@...el.com, 
	mgorman@...hsingularity.net, david@...hat.com, peterx@...hat.com, 
	oleg@...hat.com, dave@...olabs.net, paulmck@...nel.org, brauner@...nel.org, 
	dhowells@...hat.com, hdanton@...a.com, hughd@...gle.com, minchan@...gle.com, 
	jannh@...gle.com, souravpanda@...gle.com, pasha.tatashin@...een.com, 
	corbet@....net, linux-doc@...r.kernel.org, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v4 0/5] move per-vma lock into vm_area_struct

On Fri, Nov 22, 2024 at 3:57 AM Lorenzo Stoakes
<lorenzo.stoakes@...cle.com> wrote:
>
> On Thu, Nov 21, 2024 at 02:00:46AM +0000, Matthew Wilcox wrote:
> > On Wed, Nov 20, 2024 at 02:10:44PM -0800, Shakeel Butt wrote:
> > > If 'struct vm_area_struct' is prone to performance issues due to
> > > cacheline misalignments then we should do something about the
> > > __randomize_layout tag for it. I imagine we can identify the fields
> > > which might be performance critical to be on same cacheline or different
> > > cacheline due to false sharing then we can divide the fields into
> > > different cacheline groups and fields can be __randomize_layout within
> > > the group. WDYT?
> >
> > Pretty sure the people who think security is more important than
> > performance are the only ones who randomize structs.
>
> I agree that I don't think we need concern ourselves with users of this
> setting for precisely this reason.
>
> I wouldn't want supporting this to cause difficulty for users who do not
> enable this when those who do aren't really concerned about the perf issues
> as Matthew says.

Ack. Will keep it as is. Thanks!