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Re: [Qemu-devel] [PATCH] Call MADV_HUGEPAGE for guest RAM allocations
From: |
Aurelien Jarno |
Subject: |
Re: [Qemu-devel] [PATCH] Call MADV_HUGEPAGE for guest RAM allocations |
Date: |
Sun, 21 Oct 2012 05:46:25 +0200 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Mon, Oct 15, 2012 at 03:57:54PM -0300, Luiz Capitulino wrote:
> On Fri, 5 Oct 2012 16:47:57 -0300
> Luiz Capitulino <address@hidden> wrote:
>
> > This makes it possible for QEMU to use transparent huge pages (THP)
> > when transparent_hugepage/enabled=madvise. Otherwise THP is only
> > used when it's enabled system wide.
> >
> > Signed-off-by: Luiz Capitulino <address@hidden>
>
> ping?
>
> > ---
> > exec.c | 1 +
> > osdep.h | 5 +++++
> > 2 files changed, 6 insertions(+)
> >
> > diff --git a/exec.c b/exec.c
> > index 1114a09..7504909 100644
> > --- a/exec.c
> > +++ b/exec.c
> > @@ -2584,6 +2584,7 @@ ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size,
> > void *host,
> > cpu_physical_memory_set_dirty_range(new_block->offset, size, 0xff);
> >
> > qemu_ram_setup_dump(new_block->host, size);
> > + qemu_madvise(new_block->host, size, QEMU_MADV_HUGEPAGE);
> >
> > if (kvm_enabled())
> > kvm_setup_guest_memory(new_block->host, size);
> > diff --git a/osdep.h b/osdep.h
> > index cb213e0..c5fd3d9 100644
> > --- a/osdep.h
> > +++ b/osdep.h
> > @@ -108,6 +108,11 @@ void qemu_vfree(void *ptr);
> > #else
> > #define QEMU_MADV_DONTDUMP QEMU_MADV_INVALID
> > #endif
> > +#ifdef MADV_HUGEPAGE
> > +#define QEMU_MADV_HUGEPAGE MADV_HUGEPAGE
> > +#else
> > +#define QEMU_MADV_HUGEPAGE QEMU_MADV_INVALID
> > +#endif
> >
> > #elif defined(CONFIG_POSIX_MADVISE)
> >
>
I don't know this part of QEMU very well, so I tried to compare with how
it was done for KSM. I found two main differences:
- In the case of -mem-path QEMU doesn't try to mark the pages as
mergeable.
- An option (-machine mem-merge=false/true) is provided to enable KSM,
defaulting to true.
I am not sure if it makes sense for hugepages, but providing a
mem-huge=false/true defaulting to true might be a good idea.
--
Aurelien Jarno GPG: 1024D/F1BCDB73
address@hidden http://www.aurel32.net