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authorHugh Dickins <hugh@veritas.com>2005-10-29 18:16:18 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2005-10-29 21:40:39 -0700
commit365e9c87a982c03d0af3886e29d877f581b59611 (patch)
treed06c1918ca9fe6677d7e4e869555e095004274f7 /mm/fremap.c
parent861f2fb8e796022b4928cab9c74fca6681a1c557 (diff)
downloadlinux-365e9c87a982c03d0af3886e29d877f581b59611.tar.gz
[PATCH] mm: update_hiwaters just in time
update_mem_hiwater has attracted various criticisms, in particular from those concerned with mm scalability. Originally it was called whenever rss or total_vm got raised. Then many of those callsites were replaced by a timer tick call from account_system_time. Now Frank van Maarseveen reports that to be found inadequate. How about this? Works for Frank. Replace update_mem_hiwater, a poor combination of two unrelated ops, by macros update_hiwater_rss and update_hiwater_vm. Don't attempt to keep mm->hiwater_rss up to date at timer tick, nor every time we raise rss (usually by 1): those are hot paths. Do the opposite, update only when about to lower rss (usually by many), or just before final accounting in do_exit. Handle mm->hiwater_vm in the same way, though it's much less of an issue. Demand that whoever collects these hiwater statistics do the work of taking the maximum with rss or total_vm. And there has been no collector of these hiwater statistics in the tree. The new convention needs an example, so match Frank's usage by adding a VmPeak line above VmSize to /proc/<pid>/status, and also a VmHWM line above VmRSS (High-Water-Mark or High-Water-Memory). There was a particular anomaly during mremap move, that hiwater_vm might be captured too high. A fleeting such anomaly remains, but it's quickly corrected now, whereas before it would stick. What locking? None: if the app is racy then these statistics will be racy, it's not worth any overhead to make them exact. But whenever it suits, hiwater_vm is updated under exclusive mmap_sem, and hiwater_rss under page_table_lock (for now) or with preemption disabled (later on): without going to any trouble, minimize the time between reading current values and updating, to minimize those occasions when a racing thread bumps a count up and back down in between. Signed-off-by: Hugh Dickins <hugh@veritas.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'mm/fremap.c')
-rw-r--r--mm/fremap.c4
1 files changed, 3 insertions, 1 deletions
diff --git a/mm/fremap.c b/mm/fremap.c
index 7f08d10ceaf..49719a35769 100644
--- a/mm/fremap.c
+++ b/mm/fremap.c
@@ -143,8 +143,10 @@ int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma,
if (!pte)
goto err_unlock;
- if (!pte_none(*pte) && zap_pte(mm, vma, addr, pte))
+ if (!pte_none(*pte) && zap_pte(mm, vma, addr, pte)) {
+ update_hiwater_rss(mm);
dec_mm_counter(mm, file_rss);
+ }
set_pte_at(mm, addr, pte, pgoff_to_pte(pgoff));
pte_val = *pte;