From: Peter Xu <peterx@redhat.com>
To: David Hildenbrand <david@redhat.com>
Cc: "Marcel Apfelbaum" <mapfelba@redhat.com>,
"Cornelia Huck" <cohuck@redhat.com>,
"Eduardo Habkost" <ehabkost@redhat.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
"Stefan Weil" <sw@weilnetz.de>,
"Murilo Opsfelder Araujo" <muriloo@linux.ibm.com>,
"Richard Henderson" <richard.henderson@linaro.org>,
"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
"Juan Quintela" <quintela@redhat.com>,
qemu-devel@nongnu.org, "Halil Pasic" <pasic@linux.ibm.com>,
"Christian Borntraeger" <borntraeger@de.ibm.com>,
"Greg Kurz" <groug@kaod.org>,
"Stefan Hajnoczi" <stefanha@redhat.com>,
"Igor Mammedov" <imammedo@redhat.com>,
"Thomas Huth" <thuth@redhat.com>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Philippe Mathieu-Daudé" <philmd@redhat.com>,
"Igor Kotrasinski" <i.kotrasinsk@partner.samsung.com>
Subject: Re: [PATCH v3 02/12] softmmu/physmem: Fix ram_block_discard_range() to handle shared anonymous memory
Date: Thu, 11 Mar 2021 12:11:53 -0500 [thread overview]
Message-ID: <20210311171153.GF194839@xz-x1> (raw)
In-Reply-To: <df216a57-d45a-9563-5e88-0f2ebf6b0a7e@redhat.com>
On Thu, Mar 11, 2021 at 05:45:46PM +0100, David Hildenbrand wrote:
> On 11.03.21 17:39, Dr. David Alan Gilbert wrote:
> > * David Hildenbrand (david@redhat.com) wrote:
> > > We can create shared anonymous memory via
> > > "-object memory-backend-ram,share=on,..."
> > > which is, for example, required by PVRDMA for mremap() to work.
> > >
> > > Shared anonymous memory is weird, though. Instead of MADV_DONTNEED, we
> > > have to use MADV_REMOVE. MADV_DONTNEED fails silently and does nothing.
> >
> > OK, I wonder how stable these rules are; is it defined anywhere that
> > it's required?
> >
>
> I had a look at the Linux implementation: it's essentially shmem ... but we
> don't have an fd exposed, so we cannot use fallocate() ... :)
>
> MADV_REMOVE documents (man):
>
> "In the initial implementation, only tmpfs(5) was supported MADV_REMOVE; but
> since Linux 3.5, any filesystem which supports the fallocate(2)
> FALLOC_FL_PUNCH_HOLE mode also supports MADV_REMOVE."
Hmm, I see that MADV_DONTNEED will still tear down all mappings even for
anonymous shmem.. what did I miss?
--
Peter Xu
next prev parent reply other threads:[~2021-03-11 17:18 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-08 15:05 [PATCH v3 00/12] RAM_NORESERVE, MAP_NORESERVE and hostmem "reserve" property David Hildenbrand
2021-03-08 15:05 ` [PATCH v3 01/12] softmmu/physmem: Mark shared anonymous memory RAM_SHARED David Hildenbrand
2021-03-08 15:05 ` [PATCH v3 02/12] softmmu/physmem: Fix ram_block_discard_range() to handle shared anonymous memory David Hildenbrand
2021-03-11 16:39 ` Dr. David Alan Gilbert
2021-03-11 16:45 ` David Hildenbrand
2021-03-11 17:11 ` Peter Xu [this message]
2021-03-11 17:15 ` David Hildenbrand
2021-03-11 17:18 ` David Hildenbrand
2021-03-11 17:22 ` Peter Xu
2021-03-11 17:41 ` David Hildenbrand
2021-03-11 21:25 ` Peter Xu
2021-03-11 21:37 ` Peter Xu
2021-03-11 21:49 ` David Hildenbrand
2021-03-08 15:05 ` [PATCH v3 03/12] softmmu/physmem: Fix qemu_ram_remap() " David Hildenbrand
2021-03-08 15:05 ` [PATCH v3 04/12] util/mmap-alloc: Factor out calculation of the pagesize for the guard page David Hildenbrand
2021-03-08 15:05 ` [PATCH v3 05/12] util/mmap-alloc: Factor out reserving of a memory region to mmap_reserve() David Hildenbrand
2021-03-08 15:05 ` [PATCH v3 06/12] util/mmap-alloc: Factor out activating of memory to mmap_activate() David Hildenbrand
2021-03-08 15:05 ` [PATCH v3 07/12] softmmu/memory: Pass ram_flags into qemu_ram_alloc_from_fd() David Hildenbrand
2021-03-08 15:05 ` [PATCH v3 08/12] softmmu/memory: Pass ram_flags into memory_region_init_ram_shared_nomigrate() David Hildenbrand
2021-03-08 15:05 ` [PATCH v3 09/12] util/mmap-alloc: Pass flags instead of separate bools to qemu_ram_mmap() David Hildenbrand
2021-03-09 20:04 ` Peter Xu
2021-03-09 20:27 ` David Hildenbrand
2021-03-09 20:58 ` Peter Xu
2021-03-10 8:41 ` David Hildenbrand
2021-03-10 10:11 ` David Hildenbrand
2021-03-10 10:55 ` David Hildenbrand
2021-03-10 16:27 ` Peter Xu
2021-03-08 15:05 ` [PATCH v3 10/12] memory: introduce RAM_NORESERVE and wire it up in qemu_ram_mmap() David Hildenbrand
2021-03-08 15:05 ` David Hildenbrand
2021-03-08 15:05 ` [PATCH v3 11/12] util/mmap-alloc: Support RAM_NORESERVE via MAP_NORESERVE David Hildenbrand
2021-03-10 10:28 ` David Hildenbrand
2021-03-08 15:06 ` [PATCH v3 12/12] hostmem: Wire up RAM_NORESERVE via "reserve" property David Hildenbrand
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