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authorHugh Dickins <hughd@google.com>2017-09-09 21:27:32 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-01-05 15:44:24 +0100
commit3e3d38fd9832e82a8cb1a5b1154acfa43ac08d15 (patch)
tree6b0edf16bdce2168a41eeb58603cefd612ff84b9 /include
parentb9d2ccc54e17b5aa50dd0c036d3f4fb4e5248d54 (diff)
kaiser: vmstat show NR_KAISERTABLE as nr_overhead
The kaiser update made an interesting choice, never to free any shadow page tables. Contention on global spinlock was worrying, particularly with it held across page table scans when freeing. Something had to be done: I was going to add refcounting; but simply never to free them is an appealing choice, minimizing contention without complicating the code (the more a page table is found already, the less the spinlock is used). But leaking pages in this way is also a worry: can we get away with it? At the very least, we need a count to show how bad it actually gets: in principle, one might end up wasting about 1/256 of memory that way (1/512 for when direct-mapped pages have to be user-mapped, plus 1/512 for when they are user-mapped from the vmalloc area on another occasion (but we don't have vmalloc'ed stacks, so only large ldts are vmalloc'ed). Add per-cpu stat NR_KAISERTABLE: including 256 at startup for the shared pgd entries, and 1 for each intermediate page table added thereafter for user-mapping - but leave out the 1 per mm, for its shadow pgd, because that distracts from the monotonic increase. Shown in /proc/vmstat as nr_overhead (0 if kaiser not enabled). In practice, it doesn't look so bad so far: more like 1/12000 after nine hours of gtests below; and movable pageblock segregation should tend to cluster the kaiser tables into a subset of the address space (if not, they will be bad for compaction too). But production may tell a different story: keep an eye on this number, and bring back lighter freeing if it gets out of control (maybe a shrinker). Signed-off-by: Hugh Dickins <hughd@google.com> Acked-by: Jiri Kosina <jkosina@suse.cz> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'include')
-rw-r--r--include/linux/mmzone.h3
1 files changed, 2 insertions, 1 deletions
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index ff88d6189411..b93b578cfa42 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -131,8 +131,9 @@ enum zone_stat_item {
NR_SLAB_RECLAIMABLE,
NR_SLAB_UNRECLAIMABLE,
NR_PAGETABLE, /* used for pagetables */
- NR_KERNEL_STACK,
/* Second 128 byte cacheline */
+ NR_KERNEL_STACK,
+ NR_KAISERTABLE,
NR_UNSTABLE_NFS, /* NFS unstable pages */
NR_BOUNCE,
NR_VMSCAN_WRITE,