[Xen-changelog] [xen stable-4.6] x86/PoD: skip eager reclaim when possible

[patchbot@xxxxxxx]

commit ab2d455dcd06d19b4f6755bf406ee7302e879c02
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Fri May 27 14:41:56 2016 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri May 27 14:41:56 2016 +0200

    x86/PoD: skip eager reclaim when possible
    
    Reclaiming pages is pointless when the cache can already satisfy all
    outstanding PoD entries, and doing reclaims in that case can be very
    harmful to performance when that memory gets used by the guest, but
    only to store zeroes there.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Release-acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>
    Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxxx>
    master commit: 556c69f4efb09dd06e6bce4cbb0455287f19d02e
    master date: 2016-05-12 18:02:21 +0200
---
 xen/arch/x86/mm/p2m-pod.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/mm/p2m-pod.c b/xen/arch/x86/mm/p2m-pod.c
index 0091802..a08cfef 100644
--- a/xen/arch/x86/mm/p2m-pod.c
+++ b/xen/arch/x86/mm/p2m-pod.c
@@ -1003,7 +1003,6 @@ static void pod_eager_record(struct p2m_domain *p2m,
 {
     struct pod_mrp_list *mrp = &p2m->pod.mrp;
 
-    ASSERT(mrp->list[mrp->idx] == INVALID_GFN);
     ASSERT(gfn != INVALID_GFN);
 
     mrp->list[mrp->idx++] =
@@ -1051,7 +1050,9 @@ p2m_pod_demand_populate(struct p2m_domain *p2m, unsigned 
long gfn,
         return 0;
     }
 
-    pod_eager_reclaim(p2m);
+    /* Only reclaim if we're in actual need of more cache. */
+    if ( p2m->pod.entry_count > p2m->pod.count )
+        pod_eager_reclaim(p2m);
 
     /* Only sweep if we're actually out of memory.  Doing anything else
      * causes unnecessary time and fragmentation of superpages in the p2m. */
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.6

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