From: Feng Tang <feng.tang@xxxxxxxxx>
Subject: proc/meminfo: avoid open coded reading of vm_committed_as
Patch series "make vm_committed_as_batch aware of vm overcommit policy", v6.
When checking a performance change for will-it-scale scalability mmap test
[1], we found very high lock contention for spinlock of percpu counter
'vm_committed_as':
94.14% 0.35% [kernel.kallsyms] [k] _raw_spin_lock_irqsave
48.21% _raw_spin_lock_irqsave;percpu_counter_add_batch;__vm_enough_memory;mmap_region;do_mmap;
45.91% _raw_spin_lock_irqsave;percpu_counter_add_batch;__do_munmap;
Actually this heavy lock contention is not always necessary. The
'vm_committed_as' needs to be very precise when the strict
OVERCOMMIT_NEVER policy is set, which requires a rather small batch number
for the percpu counter.
So keep 'batch' number unchanged for strict OVERCOMMIT_NEVER policy, and
enlarge it for not-so-strict OVERCOMMIT_ALWAYS and OVERCOMMIT_GUESS
policies.
Benchmark with the same testcase in [1] shows 53% improvement on a 8C/16T
desktop, and 2097%(20X) on a 4S/72C/144T server. And for that case,
whether it shows improvements depends on if the test mmap size is bigger
than the batch number computed.
We tested 10+ platforms in 0day (server, desktop and laptop). If we lift
it to 64X, 80%+ platforms show improvements, and for 16X lift, 1/3 of the
platforms will show improvements.
And generally it should help the mmap/unmap usage,as Michal Hocko
mentioned:
: I believe that there are non-synthetic worklaods which would benefit
: from a larger batch. E.g. large in memory databases which do large
: mmaps during startups from multiple threads.
Note: There are some style complain from checkpatch for patch 4, as sysctl
handler declaration follows the similar format of sibling functions
[1] https://lore.kernel.org/lkml/20200305062138.GI5972@shao2-debian/
This patch (of 4):
Use the existing vm_memory_committed() instead, which is also convenient
for future change.
Link: http://lkml.kernel.org/r/1594389708-60781-1-git-send-email-feng.tang@xxxxxxxxx
Link: http://lkml.kernel.org/r/1594389708-60781-2-git-send-email-feng.tang@xxxxxxxxx
Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Qian Cai <cai@xxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Andi Kleen <andi.kleen@xxxxxxxxx>
Cc: Tim Chen <tim.c.chen@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Huang Ying <ying.huang@xxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Dennis Zhou <dennis@xxxxxxxxxx>
Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
Cc: kernel test robot <rong.a.chen@xxxxxxxxx>
Cc: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/proc/meminfo.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/fs/proc/meminfo.c~proc-meminfo-avoid-open-coded-reading-of-vm_committed_as
+++ a/fs/proc/meminfo.c
@@ -41,7 +41,7 @@ static int meminfo_proc_show(struct seq_
si_meminfo(&i);
si_swapinfo(&i);
- committed = percpu_counter_read_positive(&vm_committed_as);
+ committed = vm_memory_committed();
cached = global_node_page_state(NR_FILE_PAGES) -
total_swapcache_pages() - i.bufferram;
_
