From: Suren Baghdasaryan <surenb@google.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Jann Horn <jannh@google.com>, Minchan Kim <minchan@kernel.org>,
Christoph Hellwig <hch@lst.de>,
Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@kernel.org>, Michal Hocko <mhocko@suse.com>,
David Rientjes <rientjes@google.com>,
Matthew Wilcox <willy@infradead.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Roman Gushchin <guro@fb.com>, Rik van Riel <riel@surriel.com>,
Christian Brauner <christian@brauner.io>,
Oleg Nesterov <oleg@redhat.com>,
Tim Murray <timmurray@google.com>,
Linux API <linux-api@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
kernel list <linux-kernel@vger.kernel.org>,
kernel-team <kernel-team@android.com>
Subject: Re: [PATCH 1/2] mm/madvise: allow process_madvise operations on entire memory range
Date: Tue, 22 Dec 2020 09:48:43 -0800 [thread overview]
Message-ID: <CAJuCfpGiVS69kznSrAdosxnRd-zgXPJd8MXou=gd8K8j7xLMjA@mail.gmail.com> (raw)
In-Reply-To: <20201222134438.GA7170@infradead.org>
On Tue, Dec 22, 2020 at 5:44 AM Christoph Hellwig <hch@infradead.org> wrote:
>
> On Fri, Dec 11, 2020 at 09:27:46PM +0100, Jann Horn wrote:
> > > Can we just use one element in iovec to indicate entire address rather
> > > than using up the reserved flags?
> > >
> > > struct iovec {
> > > .iov_base = NULL,
> > > .iov_len = (~(size_t)0),
> > > };
> >
> > In addition to Suren's objections, I think it's also worth considering
> > how this looks in terms of compat API. If a compat process does
> > process_madvise() on another compat process, it would be specifying
> > the maximum 32-bit number, rather than the maximum 64-bit number, so
> > you'd need special code to catch that case, which would be ugly.
> >
> > And when a compat process uses this API on a non-compat process, it
> > semantically gets really weird: The actual address range covered would
> > be larger than the address range specified.
> >
> > And if we want different access checks for the two flavors in the
> > future, gating that different behavior on special values in the iovec
> > would feel too magical to me.
> >
> > And the length value SIZE_MAX doesn't really make sense anyway because
> > the length of the whole address space would be SIZE_MAX+1, which you
> > can't express.
> >
> > So I'm in favor of a new flag, and strongly against using SIZE_MAX as
> > a magic number here.
>
> Yes, using SIZE_MAX is a horrible interface in this case. I'm not
> a huge fan of a flag either. What is the use case for the madvise
> to all of a processes address space anyway?
Thanks for the feedback! The use case is userspace memory reaping
similar to oom-reaper. Detailed justification is here:
https://lore.kernel.org/linux-mm/20201124053943.1684874-1-surenb@google.com
next prev parent reply other threads:[~2020-12-22 17:48 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-24 5:39 [PATCH 0/2] userspace memory reaping using process_madvise Suren Baghdasaryan
2020-11-24 5:39 ` [PATCH 1/2] mm/madvise: allow process_madvise operations on entire memory range Suren Baghdasaryan
2020-11-25 23:13 ` Minchan Kim
2020-11-25 23:23 ` Suren Baghdasaryan
2020-11-25 23:43 ` Minchan Kim
2020-11-30 19:01 ` Suren Baghdasaryan
2020-12-08 7:23 ` Suren Baghdasaryan
2020-12-11 20:27 ` Jann Horn
2020-12-11 23:01 ` Minchan Kim
2020-12-12 0:16 ` Jann Horn
2020-12-22 13:44 ` Christoph Hellwig
2020-12-22 17:48 ` Suren Baghdasaryan [this message]
2020-12-23 4:09 ` Suren Baghdasaryan
2020-12-23 7:57 ` Christoph Hellwig
2020-12-23 17:32 ` Suren Baghdasaryan
2020-11-24 5:39 ` [PATCH 2/2] mm/madvise: add process_madvise MADV_DONTNEER support Suren Baghdasaryan
2020-11-24 13:42 ` Oleg Nesterov
2020-11-24 16:42 ` Suren Baghdasaryan
2020-12-08 23:40 ` Jann Horn
2020-12-08 23:59 ` Suren Baghdasaryan
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