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/rmap.c | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'mm/rmap.c') diff --git a/mm/rmap.c b/mm/rmap.c index f69d5342ce7f..4c52c56c9905 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -538,6 +538,9 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma) if (pte_dirty(pteval)) set_page_dirty(page); + /* Update high watermark before we lower rss */ + update_hiwater_rss(mm); + if (PageAnon(page)) { swp_entry_t entry = { .val = page->private }; /* @@ -628,6 +631,9 @@ static void try_to_unmap_cluster(unsigned long cursor, if (!pmd_present(*pmd)) goto out_unlock; + /* Update high watermark before we lower rss */ + update_hiwater_rss(mm); + for (original_pte = pte = pte_offset_map(pmd, address); address < end; pte++, address += PAGE_SIZE) { -- cgit v1.2.3-59-g8ed1b