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* [PATCH] x86/mem_sharing: don't lock parent during fork reset
@ 2021-09-16 15:04 Tamas K Lengyel
  2021-09-17  7:26 ` Jan Beulich
  0 siblings, 1 reply; 4+ messages in thread
From: Tamas K Lengyel @ 2021-09-16 15:04 UTC (permalink / raw)
  To: xen-devel
  Cc: Tamas K Lengyel, Tamas K Lengyel, Jan Beulich, Andrew Cooper,
	George Dunlap, Roger Pau Monné,
	Wei Liu

During fork reset operation the parent domain doesn't need to be gathered using
rcu_lock_live_remote_domain_by_id as the fork reset doesn't modify anything on
the parent. The parent is also guaranteed to be paused while forks are active.
This patch reduces lock contention when performing resets in parallel.

Signed-off-by: Tamas K Lengyel <tamas.lengyel@intel.com>
---
 xen/arch/x86/mm/mem_sharing.c | 13 +++----------
 1 file changed, 3 insertions(+), 10 deletions(-)

diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
index 8d5d44bdbc..b80b978ef3 100644
--- a/xen/arch/x86/mm/mem_sharing.c
+++ b/xen/arch/x86/mm/mem_sharing.c
@@ -1879,9 +1879,10 @@ static int fork(struct domain *cd, struct domain *d)
  * 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)
+static int mem_sharing_fork_reset(struct domain *d)
 {
     int rc;
+    struct domain *pd = d->parent;
     struct p2m_domain *p2m = p2m_get_hostp2m(d);
     struct page_info *page, *tmp;
 
@@ -2226,8 +2227,6 @@ int mem_sharing_memop(XEN_GUEST_HANDLE_PARAM(xen_mem_sharing_op_t) arg)
 
     case XENMEM_sharing_op_fork_reset:
     {
-        struct domain *pd;
-
         rc = -EINVAL;
         if ( mso.u.fork.pad || mso.u.fork.flags )
             goto out;
@@ -2236,13 +2235,7 @@ int mem_sharing_memop(XEN_GUEST_HANDLE_PARAM(xen_mem_sharing_op_t) arg)
         if ( !d->parent )
             goto out;
 
-        rc = rcu_lock_live_remote_domain_by_id(d->parent->domain_id, &pd);
-        if ( rc )
-            goto out;
-
-        rc = mem_sharing_fork_reset(d, pd);
-
-        rcu_unlock_domain(pd);
+        rc = mem_sharing_fork_reset(d);
         break;
     }
 
-- 
2.25.1



^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2021-09-20  8:14 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-09-16 15:04 [PATCH] x86/mem_sharing: don't lock parent during fork reset Tamas K Lengyel
2021-09-17  7:26 ` Jan Beulich
2021-09-17 14:21   ` Tamas K Lengyel
2021-09-20  8:14     ` Jan Beulich

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