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Re: [Qemu-devel] [PATCH v2] add -machine mem_merge=on|off option
From: |
Luiz Capitulino |
Subject: |
Re: [Qemu-devel] [PATCH v2] add -machine mem_merge=on|off option |
Date: |
Fri, 29 Jun 2012 11:21:48 -0300 |
On Fri, 29 Jun 2012 09:18:09 -0500
Anthony Liguori <address@hidden> wrote:
> On 06/29/2012 09:00 AM, Luiz Capitulino wrote:
> > Allows to disable memory merge support (KSM on Linux), which is enabled
> > by default otherwise.
> >
> > Signed-off-by: Luiz Capitulino<address@hidden>
> > ---
> >
> > o v2: improve manpage description
> >
> > exec.c | 19 ++++++++++++++++---
> > qemu-config.c | 4 ++++
> > qemu-options.hx | 7 ++++++-
> > 3 files changed, 26 insertions(+), 4 deletions(-)
> >
> > diff --git a/exec.c b/exec.c
> > index 8244d54..24dd154 100644
> > --- a/exec.c
> > +++ b/exec.c
> > @@ -2499,6 +2499,19 @@ void qemu_ram_set_idstr(ram_addr_t addr, const char
> > *name, DeviceState *dev)
> > }
> > }
> >
> > +static int madvise_mergeable(void *addr, size_t len)
> > +{
> > + QemuOpts *opts;
> > +
> > + opts = qemu_opts_find(qemu_find_opts("machine"), 0);
> > + if (opts&& !qemu_opt_get_bool(opts, "mem_merge", true)) {
> > + /* disabled by the user */
> > + return 0;
> > + }
> > +
> > + return qemu_madvise(addr, len, QEMU_MADV_MERGEABLE);
> > +}
> > +
> > ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
> > MemoryRegion *mr)
> > {
> > @@ -2518,7 +2531,7 @@ ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size,
> > void *host,
> > new_block->host = file_ram_alloc(new_block, size, mem_path);
> > if (!new_block->host) {
> > new_block->host = qemu_vmalloc(size);
> > - qemu_madvise(new_block->host, size, QEMU_MADV_MERGEABLE);
> > + madvise_mergeable(new_block->host, size);
>
> Just a style thing. Having a function call that may silently not do what you
> expect it to do is an unfriendly thing.
>
> You should at least name the function something like
> 'memory_try_enable_merging'
>
> Maybe that's not the best name, but you get the idea at least.
Agreed, will rename and post v3.
>
> Regards,
>
> Anthony Liguori
>
> > }
> > #else
> > fprintf(stderr, "-mem-path option unsupported\n");
> > @@ -2545,7 +2558,7 @@ ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size,
> > void *host,
> > new_block->host = qemu_vmalloc(size);
> > }
> > #endif
> > - qemu_madvise(new_block->host, size, QEMU_MADV_MERGEABLE);
> > + madvise_mergeable(new_block->host, size);
> > }
> > }
> > new_block->length = size;
> > @@ -2672,7 +2685,7 @@ void qemu_ram_remap(ram_addr_t addr, ram_addr_t
> > length)
> > length, addr);
> > exit(1);
> > }
> > - qemu_madvise(vaddr, length, QEMU_MADV_MERGEABLE);
> > + madvise_mergeable(vaddr, length);
> > }
> > return;
> > }
> > diff --git a/qemu-config.c b/qemu-config.c
> > index 5c3296b..e47612e 100644
> > --- a/qemu-config.c
> > +++ b/qemu-config.c
> > @@ -595,6 +595,10 @@ static QemuOptsList qemu_machine_opts = {
> > .name = "dt_compatible",
> > .type = QEMU_OPT_STRING,
> > .help = "Overrides the \"compatible\" property of the dt root
> > node",
> > + }, {
> > + .name = "mem_merge",
> > + .type = QEMU_OPT_BOOL,
> > + .help = "enable/disable memory merge support",
> > },
> > { /* End of list */ }
> > },
> > diff --git a/qemu-options.hx b/qemu-options.hx
> > index 8b66264..15351a5 100644
> > --- a/qemu-options.hx
> > +++ b/qemu-options.hx
> > @@ -33,7 +33,8 @@ DEF("machine", HAS_ARG, QEMU_OPTION_machine, \
> > " property accel=accel1[:accel2[:...]] selects
> > accelerator\n"
> > " supported accelerators are kvm, xen, tcg (default:
> > tcg)\n"
> > " kernel_irqchip=on|off controls accelerated irqchip
> > support\n"
> > - " kvm_shadow_mem=size of KVM shadow MMU\n",
> > + " kvm_shadow_mem=size of KVM shadow MMU\n"
> > + " mem_merge=on|off controls memory merge support
> > (default: on)\n",
> > QEMU_ARCH_ALL)
> > STEXI
> > @item -machine address@hidden,address@hidden,...]]
> > @@ -50,6 +51,10 @@ to initialize.
> > Enables in-kernel irqchip support for the chosen accelerator when
> > available.
> > @item kvm_shadow_mem=size
> > Defines the size of the KVM shadow MMU.
> > address@hidden mem_merge=on|off
> > +Enables or disables memory merge support. This feature, when supported by
> > +the host, de-duplicates identical memory pages among VMs instances
> > +(enabled by default).
> > @end table
> > ETEXI
> >
>