From: Guillaume Morin <guillaume@morinfr.org>
To: David Hildenbrand <david@redhat.com>
Cc: Guillaume Morin <guillaume@morinfr.org>,
oleg@redhat.com, linux-kernel@vger.kernel.org,
linux-trace-kernel@vger.kernel.org, muchun.song@linux.dev
Subject: Re: [RFC][PATCH] uprobe: support for private hugetlb mappings
Date: Wed, 24 Apr 2024 22:44:42 +0200 [thread overview]
Message-ID: <ZilvOi7ceSXmwkNq@bender.morinfr.org> (raw)
In-Reply-To: <8d5314ac-5afe-41d4-9d27-9512cd96d21c@redhat.com>
On 24 Apr 22:09, David Hildenbrand wrote:
> > > Let me try to see if we can get this done cleaner.
> > >
> > > One ugly part (in general here) is the custom page replacement in the
> > > registration part.
> > >
> > > We are guaranteed to have a MAP_PRIVATE mapping. Instead of replacing pages
> > > ourselves (which we likely shouldn't do ...) ... maybe we could use
> > > FAULT_FLAG_UNSHARE faults such that we will get an anonymous folio
> > > populated. (like KSM does nowadays)
> > >
> > > Punching FOLL_PIN|FOLL_LONGTERM into GUP would achieve the same thing, but
> > > using FOLL_WRITE would not work on many file systems. So maybe we have to
> > > trigger an unsharing fault ourselves.
>
> ^ realizing that we already use FOLL_FORCE, so we can just use FOLL_WRITE to
> break COW.
It was never clear to me why uprobes was not doing FOLL_WRITE in the
first place, I must say.
One issue here is that FOLL_FORCE|FOLL_WRITE is not implemented for
hugetlb mappings. However this was also on my TODO and I have a draft
patch that implements it.
>
> > >
> > > That would do the page replacement for us and we "should" be able to lookup
> > > an anonymous folio that we can then just modify, like ptrace would.
> > >
> > > But then, there is also unregistration part, with weird conditional page
> > > replacement. Zapping the anon page if the content matches the content of the
> > > original page is one thing. But why are we placing an existing anonymous
> > > page by a new anonymous page when the content from the original page differs
> > > (but matches the one from the just copied page?)?
> > >
> > > I'll have to further think about that one. It's all a bit nasty.
> >
> > Sounds good to me. I am willing to help with the code when you have a
> > plan or testing as you see fit. Let me know.
>
> I'm hacking on a redesign that removes the manual COW breaking logic and
> *might* make it easier to integrate hugetlb. (very likely, but until I have
> the redesign running I cannot promise anything :) )
>
> I'll let you know once I have something ready so you could integrate the
> hugetlb portion.
Sounds good.
--
Guillaume Morin <guillaume@morinfr.org>
next prev parent reply other threads:[~2024-04-24 20:44 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-19 18:37 [RFC][PATCH] uprobe: support for private hugetlb mappings Guillaume Morin
2024-04-22 9:39 ` David Hildenbrand
2024-04-22 18:11 ` Guillaume Morin
2024-04-22 18:59 ` David Hildenbrand
2024-04-22 20:53 ` Guillaume Morin
2024-04-24 20:09 ` David Hildenbrand
2024-04-24 20:44 ` Guillaume Morin [this message]
2024-04-24 21:00 ` David Hildenbrand
2024-04-25 15:19 ` Guillaume Morin
2024-04-25 15:42 ` David Hildenbrand
2024-04-25 19:56 ` David Hildenbrand
2024-04-26 0:09 ` Guillaume Morin
2024-04-26 7:19 ` David Hildenbrand
2024-04-26 19:55 ` Guillaume Morin
2024-04-30 15:22 ` Guillaume Morin
2024-04-30 18:21 ` David Hildenbrand
2024-04-30 18:58 ` Guillaume Morin
2024-04-30 19:25 ` David Hildenbrand
2024-05-02 3:59 ` Guillaume Morin
2024-05-16 17:44 ` Guillaume Morin
2024-05-16 19:52 ` David Hildenbrand
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