From: David Hildenbrand <david@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Stefan Weil <sw@weilnetz.de>,
Eduardo Habkost <ehabkost@redhat.com>,
Markus Armbruster <armbru@redhat.com>,
qemu-devel@nongnu.org,
"Dr . David Alan Gilbert" <dgilbert@redhat.com>,
Alex Williamson <alex.williamson@redhat.com>,
Murilo Opsfelder Araujo <muriloo@linux.ibm.com>,
Paolo Bonzini <pbonzini@redhat.com>, Greg Kurz <groug@kaod.org>,
Richard Henderson <rth@twiddle.net>
Subject: Re: [PATCH v1 00/13] Ram blocks with resizable anonymous allocations under POSIX
Date: Thu, 6 Feb 2020 10:45:57 +0100 [thread overview]
Message-ID: <184e2a98-69cc-ca8f-6861-abddcfe8423f@redhat.com> (raw)
In-Reply-To: <20200206042723-mutt-send-email-mst@kernel.org>
On 06.02.20 10:27, Michael S. Tsirkin wrote:
> On Mon, Feb 03, 2020 at 07:31:12PM +0100, David Hildenbrand wrote:
>> We already allow resizable ram blocks for anonymous memory, however, they
>> are not actually resized. All memory is mmaped() R/W, including the memory
>> exceeding the used_length, up to the max_length.
>>
>> When resizing, effectively only the boundary is moved. Implement actually
>> resizable anonymous allocations and make use of them in resizable ram
>> blocks when possible. Memory exceeding the used_length will be
>> inaccessible. Especially ram block notifiers require care.
>>
>> Having actually resizable anonymous allocations (via mmap-hackery) allows
>> to reserve a big region in virtual address space and grow the
>> accessible/usable part on demand. Even if "/proc/sys/vm/overcommit_memory"
>> is set to "never" under Linux, huge reservations will succeed. If there is
>> not enough memory when resizing (to populate parts of the reserved region),
>> trying to resize will fail. Only the actually used size is reserved in the
>> OS.
>>
>> E.g., virtio-mem [1] wants to reserve big resizable memory regions and
>> grow the usable part on demand. I think this change is worth sending out
>> individually. Accompanied by a bunch of minor fixes and cleanups.
>>
>> [1] https://lore.kernel.org/kvm/20191212171137.13872-1-david@redhat.com/
>
> How does this inteact with all the prealloc/mlock things designed
> for realtime?
- Prealloc: we don't support resizable ram blocks with prealloc
-- qemu_ram_alloc_from_ptr() is the only way to get "real" preallocated
ram blocks from a pointer. They are never resizable.
-- "prealloc" with memory backends (e.g., backends/hostmem.c): Memory
backends don't support resizable ram blocks yet. I have patches to
support that, and disallow prealloc for them.
-- file-based ram blocks are not resizable
- mlock
-- os_mlock() does a mlockall(MCL_CURRENT | MCL_FUTURE)
-- That should work just fine with ordinary mmap() invalidating old
mmaps and creating new mmaps(). Just like when hotplugging/unplugging
a DIMM.
Resizing currently only happens during reboot/migration. If mlock_all
would result in issues, we could fallback to old handling (if
(enable_mlock) ...) - but I don't think this is necessary.
So I don't see an issues with that :) Thanks!
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2020-02-06 9:48 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-03 18:31 [PATCH v1 00/13] Ram blocks with resizable anonymous allocations under POSIX David Hildenbrand
2020-02-03 18:31 ` [PATCH v1 01/13] util: vfio-helpers: Factor out and fix processing of existings ram blocks David Hildenbrand
2020-02-03 18:31 ` [PATCH v1 02/13] exec: Factor out setting ram settings (madvise ...) into qemu_ram_apply_settings() David Hildenbrand
2020-02-06 11:42 ` Richard Henderson
2020-02-03 18:31 ` [PATCH v1 03/13] exec: Reuse qemu_ram_apply_settings() in qemu_ram_remap() David Hildenbrand
2020-02-06 11:43 ` Richard Henderson
2020-02-03 18:31 ` [PATCH v1 04/13] exec: Drop "shared" parameter from ram_block_add() David Hildenbrand
2020-02-06 11:44 ` Richard Henderson
2020-02-03 18:31 ` [PATCH v1 05/13] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize() David Hildenbrand
2020-02-05 19:37 ` Murilo Opsfelder Araújo
2020-02-06 11:46 ` Richard Henderson
2020-02-03 18:31 ` [PATCH v1 06/13] util/mmap-alloc: Factor out reserving of a memory region to mmap_reserve() David Hildenbrand
2020-02-05 19:40 ` Murilo Opsfelder Araújo
2020-02-06 11:55 ` Richard Henderson
2020-02-06 13:16 ` David Hildenbrand
2020-02-03 18:31 ` [PATCH v1 07/13] util/mmap-alloc: Factor out populating of memory to mmap_populate() David Hildenbrand
2020-02-05 19:56 ` Murilo Opsfelder Araújo
2020-02-06 9:26 ` David Hildenbrand
2020-02-06 11:59 ` Richard Henderson
2020-02-03 18:31 ` [PATCH v1 08/13] util/mmap-alloc: Prepare for resizable mmaps David Hildenbrand
2020-02-05 23:00 ` Murilo Opsfelder Araújo
2020-02-06 8:52 ` David Hildenbrand
2020-02-06 12:31 ` Murilo Opsfelder Araújo
2020-02-06 13:16 ` David Hildenbrand
2020-02-06 15:13 ` David Hildenbrand
2020-02-06 12:02 ` Richard Henderson
2020-02-03 18:31 ` [PATCH v1 09/13] util/mmap-alloc: Implement " David Hildenbrand
2020-02-06 12:08 ` Richard Henderson
2020-02-06 13:22 ` David Hildenbrand
2020-02-06 15:27 ` David Hildenbrand
2020-02-07 0:29 ` Murilo Opsfelder Araújo
2020-02-10 9:39 ` David Hildenbrand
2020-02-03 18:31 ` [PATCH v1 10/13] numa: Introduce ram_block_notify_resized() and ram_block_notifiers_support_resize() David Hildenbrand
2020-02-03 18:31 ` [PATCH v1 11/13] util: vfio-helpers: Implement ram_block_resized() David Hildenbrand
2020-02-10 13:41 ` David Hildenbrand
2020-02-03 18:31 ` [PATCH v1 12/13] util: oslib: Resizable anonymous allocations under POSIX David Hildenbrand
2020-02-03 18:31 ` [PATCH v1 13/13] exec: Ram blocks with resizable " David Hildenbrand
2020-02-10 10:12 ` David Hildenbrand
2020-02-06 9:27 ` [PATCH v1 00/13] " Michael S. Tsirkin
2020-02-06 9:45 ` David Hildenbrand [this message]
2020-02-06 20:11 ` Dr. David Alan Gilbert
2020-02-06 20:31 ` David Hildenbrand
2020-02-07 15:28 ` Dr. David Alan Gilbert
2020-02-10 9:47 ` David Hildenbrand
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