From: "Roger Pau Monné" <roger.pau@citrix.com>
To: Tamas K Lengyel <tamas.lengyel@intel.com>
Cc: Tamas K Lengyel <tamas@tklengyel.com>,
Julien Grall <julien@xen.org>, Wei Liu <wl@xen.org>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Ian Jackson <ian.jackson@eu.citrix.com>,
George Dunlap <george.dunlap@citrix.com>,
Stefano Stabellini <sstabellini@kernel.org>,
Jan Beulich <jbeulich@suse.com>,
xen-devel@lists.xenproject.org
Subject: Re: [Xen-devel] [PATCH v12 2/3] x86/mem_sharing: reset a fork
Date: Wed, 25 Mar 2020 16:52:47 +0100 [thread overview]
Message-ID: <20200325155247.GE28601@Air-de-Roger> (raw)
In-Reply-To: <46457bd6e877abe12a8c005c23f0f1aab13afd24.1584981438.git.tamas.lengyel@intel.com>
On Mon, Mar 23, 2020 at 10:04:36AM -0700, Tamas K Lengyel wrote:
> Implement hypercall that allows a fork to shed all memory that got allocated
> for it during its execution and re-load its vCPU context from the parent VM.
> This allows the forked VM to reset into the same state the parent VM is in a
> faster way then creating a new fork would be. Measurements show about a 2x
> speedup during normal fuzzing operations. Performance may vary depending how
> much memory got allocated for the forked VM. If it has been completely
> deduplicated from the parent VM then creating a new fork would likely be more
> performant.
>
> Signed-off-by: Tamas K Lengyel <tamas.lengyel@intel.com>
LGTM:
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
One minor nit below.
> ---
> v12: remove continuation & add comment back
> address style issues pointed out by Jan
> ---
> xen/arch/x86/mm/mem_sharing.c | 77 +++++++++++++++++++++++++++++++++++
> xen/include/public/memory.h | 1 +
> 2 files changed, 78 insertions(+)
>
> diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
> index 23deeddff2..930a5f58ef 100644
> --- a/xen/arch/x86/mm/mem_sharing.c
> +++ b/xen/arch/x86/mm/mem_sharing.c
> @@ -1775,6 +1775,60 @@ static int fork(struct domain *cd, struct domain *d)
> return rc;
> }
>
> +/*
> + * The fork reset operation is intended to be used on short-lived forks only.
> + * There is no hypercall continuation operation implemented for this reason.
> + * For forks that obtain a larger memory footprint it is likely going to be
> + * more performant to create a new fork instead of resetting an existing one.
> + *
> + * TODO: In case this hypercall would become useful on forks with larger memory
> + * footprints the hypercall continuation should be implemented (or if this
> + * feature needs to be become "stable").
> + */
> +static int mem_sharing_fork_reset(struct domain *d, struct domain *pd)
> +{
> + int rc;
> + struct p2m_domain *p2m = p2m_get_hostp2m(d);
> + struct page_info *page, *tmp;
> +
> + spin_lock(&d->page_alloc_lock);
> + domain_pause(d);
> +
> + page_list_for_each_safe(page, tmp, &d->page_list)
> + {
> + p2m_type_t p2mt;
> + p2m_access_t p2ma;
> + mfn_t mfn = page_to_mfn(page);
> + gfn_t gfn = mfn_to_gfn(d, mfn);
> +
> + mfn = __get_gfn_type_access(p2m, gfn_x(gfn), &p2mt, &p2ma,
> + 0, NULL, false);
> +
> + /* only reset pages that are sharable */
> + if ( !p2m_is_sharable(p2mt) )
> + continue;
> +
> + /* take an extra reference or just skip if can't for whatever reason */
> + if ( !get_page(page, d) )
> + continue;
You can join both conditions above into a single one, if both just
need to perform a continue.
Thanks, Roger.
next prev parent reply other threads:[~2020-03-25 15:53 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-23 17:04 [Xen-devel] [PATCH v12 0/3] VM forking Tamas K Lengyel
2020-03-23 17:04 ` [Xen-devel] [PATCH v12 1/3] xen/mem_sharing: " Tamas K Lengyel
2020-03-25 15:47 ` Roger Pau Monné
2020-03-25 16:04 ` Tamas K Lengyel
2020-03-25 16:16 ` Tamas K Lengyel
2020-03-25 16:34 ` Tamas K Lengyel
2020-03-25 16:42 ` Julien Grall
2020-03-25 16:47 ` Tamas K Lengyel
2020-03-25 16:51 ` Julien Grall
2020-03-25 17:00 ` Tamas K Lengyel
2020-03-25 17:16 ` Roger Pau Monné
2020-03-25 17:47 ` Tamas K Lengyel
2020-03-25 16:54 ` Roger Pau Monné
2020-03-26 7:02 ` Jan Beulich
2020-03-26 8:42 ` Roger Pau Monné
2020-03-26 7:07 ` Jan Beulich
2020-03-26 9:10 ` Roger Pau Monné
2020-03-26 17:01 ` Tamas K Lengyel
2020-03-26 12:33 ` Jan Beulich
2020-03-26 14:52 ` Tamas K Lengyel
2020-03-23 17:04 ` [Xen-devel] [PATCH v12 2/3] x86/mem_sharing: reset a fork Tamas K Lengyel
2020-03-25 15:52 ` Roger Pau Monné [this message]
2020-03-25 15:54 ` Tamas K Lengyel
2020-03-26 10:16 ` Jan Beulich
2020-03-26 14:48 ` Tamas K Lengyel
2020-03-26 14:52 ` Jan Beulich
2020-03-26 14:53 ` Tamas K Lengyel
2020-03-26 23:40 ` Tamas K Lengyel
2020-03-23 17:04 ` [Xen-devel] [PATCH v12 3/3] xen/tools: VM forking toolstack side Tamas K Lengyel
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