From 365e9c87a982c03d0af3886e29d877f581b59611 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Sat, 29 Oct 2005 18:16:18 -0700 Subject: [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//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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/nommu.c | 15 ++------------- 1 file changed, 2 insertions(+), 13 deletions(-) (limited to 'mm/nommu.c') diff --git a/mm/nommu.c b/mm/nommu.c index 599924886eb5..dfb124ffb9be 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -931,6 +931,8 @@ int do_munmap(struct mm_struct *mm, unsigned long addr, size_t len) realalloc -= kobjsize(vml); askedalloc -= sizeof(*vml); kfree(vml); + + update_hiwater_vm(mm); mm->total_vm -= len >> PAGE_SHIFT; #ifdef DEBUG @@ -1078,19 +1080,6 @@ void arch_unmap_area(struct mm_struct *mm, unsigned long addr) { } -void update_mem_hiwater(struct task_struct *tsk) -{ - unsigned long rss; - - if (likely(tsk->mm)) { - rss = get_mm_rss(tsk->mm); - if (tsk->mm->hiwater_rss < rss) - tsk->mm->hiwater_rss = rss; - if (tsk->mm->hiwater_vm < tsk->mm->total_vm) - tsk->mm->hiwater_vm = tsk->mm->total_vm; - } -} - void unmap_mapping_range(struct address_space *mapping, loff_t const holebegin, loff_t const holelen, int even_cows) -- cgit v1.2.3-55-g7522