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Re: [PATCH v1 13/13] exec: Ram blocks with resizable anonymous allocatio
From: |
David Hildenbrand |
Subject: |
Re: [PATCH v1 13/13] exec: Ram blocks with resizable anonymous allocations under POSIX |
Date: |
Mon, 10 Feb 2020 11:12:11 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 |
On 03.02.20 19:31, David Hildenbrand wrote:
> We can now make use of resizable anonymous allocations to implement
> actually resizable ram blocks. Resizable anonymous allocations are
> not implemented under WIN32 yet and are not available when using
> alternative allocators. Fall back to the existing handling.
>
> We also have to fallback to the existing handling in case any ram block
> notifier does not support resizing (esp., AMD SEV, HAX) yet. Remember
> in RAM_RESIZEABLE_ALLOC if we are using resizable anonymous allocations.
>
> As the mmap()-hackery will invalidate some madvise settings, we have to
> re-apply them after resizing. After resizing, notify the ram block
> notifiers.
>
> The benefit of actually resizable ram blocks is that e.g., under Linux,
> only the actual size will be reserved (even if
> "/proc/sys/vm/overcommit_memory" is set to "never"). Additional memory will
> be reserved when trying to resize, which allows to have ram blocks that
> start small but can theoretically grow very large.
>
> Cc: Richard Henderson <address@hidden>
> Cc: Paolo Bonzini <address@hidden>
> Cc: "Dr. David Alan Gilbert" <address@hidden>
> Cc: Eduardo Habkost <address@hidden>
> Cc: Marcel Apfelbaum <address@hidden>
> Cc: Stefan Weil <address@hidden>
> Signed-off-by: David Hildenbrand <address@hidden>
> ---
> exec.c | 68 +++++++++++++++++++++++++++++++++++----
> hw/core/numa.c | 10 ++++--
> include/exec/cpu-common.h | 2 ++
> include/exec/memory.h | 8 +++++
> 4 files changed, 79 insertions(+), 9 deletions(-)
>
> diff --git a/exec.c b/exec.c
> index fc65c4f7ca..a59d1efde3 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2053,6 +2053,16 @@ void qemu_ram_unset_migratable(RAMBlock *rb)
> rb->flags &= ~RAM_MIGRATABLE;
> }
>
> +bool qemu_ram_is_resizable(RAMBlock *rb)
> +{
> + return rb->flags & RAM_RESIZEABLE;
> +}
> +
> +bool qemu_ram_is_resizable_alloc(RAMBlock *rb)
> +{
> + return rb->flags & RAM_RESIZEABLE_ALLOC;
> +}
> +
> /* Called with iothread lock held. */
> void qemu_ram_set_idstr(RAMBlock *new_block, const char *name, DeviceState
> *dev)
> {
> @@ -2139,6 +2149,8 @@ static void qemu_ram_apply_settings(void *host, size_t
> length)
> */
> int qemu_ram_resize(RAMBlock *block, ram_addr_t newsize, Error **errp)
> {
> + const uint64_t oldsize = block->used_length;
> +
> assert(block);
>
> newsize = HOST_PAGE_ALIGN(newsize);
> @@ -2147,7 +2159,7 @@ int qemu_ram_resize(RAMBlock *block, ram_addr_t
> newsize, Error **errp)
> return 0;
> }
>
> - if (!(block->flags & RAM_RESIZEABLE)) {
> + if (!qemu_ram_is_resizable(block)) {
> error_setg_errno(errp, EINVAL,
> "Length mismatch: %s: 0x" RAM_ADDR_FMT
> " in != 0x" RAM_ADDR_FMT, block->idstr,
> @@ -2163,10 +2175,26 @@ int qemu_ram_resize(RAMBlock *block, ram_addr_t
> newsize, Error **errp)
> return -EINVAL;
> }
>
> + if (qemu_ram_is_resizable_alloc(block)) {
> + g_assert(ram_block_notifiers_support_resize());
> + if (qemu_anon_ram_resize(block->host, block->used_length,
> + newsize, block->flags & RAM_SHARED) ==
> NULL) {
> + error_setg_errno(errp, -ENOMEM,
> + "Could not allocate enough memory.");
> + return -ENOMEM;
> + }
> + }
> +
I'll most probably rework to have separate paths when growing/shrinking,
with a different sequence of steps. (e.g., perform actual shrinking as
last step, so all mappings remain valid, and ignore errors (which are
unlikely either way)).
--
Thanks,
David / dhildenb
- Re: [PATCH v1 08/13] util/mmap-alloc: Prepare for resizable mmaps, (continued)
- [PATCH v1 11/13] util: vfio-helpers: Implement ram_block_resized(), David Hildenbrand, 2020/02/03
- [PATCH v1 12/13] util: oslib: Resizable anonymous allocations under POSIX, David Hildenbrand, 2020/02/03
- [PATCH v1 06/13] util/mmap-alloc: Factor out reserving of a memory region to mmap_reserve(), David Hildenbrand, 2020/02/03
- [PATCH v1 13/13] exec: Ram blocks with resizable anonymous allocations under POSIX, David Hildenbrand, 2020/02/03
- Re: [PATCH v1 13/13] exec: Ram blocks with resizable anonymous allocations under POSIX,
David Hildenbrand <=
- Re: [PATCH v1 00/13] Ram blocks with resizable anonymous allocations under POSIX, Michael S. Tsirkin, 2020/02/06
- Re: [PATCH v1 00/13] Ram blocks with resizable anonymous allocations under POSIX, Dr. David Alan Gilbert, 2020/02/06