From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 3 Sep 2007 21:58:47 +0200 From: Nick Piggin Subject: [patch][rfc] delayacct: fix swapin delay accounting (maybe) Message-ID: <20070903195847.GD24413@wotan.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: owner-linux-mm@kvack.org Return-Path: To: Shailabh Nagar , Hugh Dickins , Linux Memory Management List List-ID: Hi, I can't convince myself that delay accounting for swapin is quite right at the moment (not having a test setup handy to run and check for myself). Maybe I'm not reading the swapin code very well... lookup_swap_cache, and read_swap_cache_async should be non-blocking operations for the most part. read_swap_cache_async might, when allocating the new page, go into reclaim and take a long time to come back. However is that any more a "swapin" delay than eg. when we sleep on mmap_sem when first taking the fault, or any other types of fault which require allocations? None of which we account for as swapin delay. But the most obvious delay, where we actually lock the page waiting for the swap IO to finish, does not seem to be accounted at all! My proposed fix is to just move the swaping delay accounting to the point where the VM does actually wait, for the swapin. I have no idea what uses swapin delay accounting, but it would be good to see if this makes a positive (or at least not negative) impact on those users... Thanks, Nick -- Index: linux-2.6/mm/memory.c =================================================================== --- linux-2.6.orig/mm/memory.c +++ linux-2.6/mm/memory.c @@ -2158,7 +2158,6 @@ static int do_swap_page(struct mm_struct migration_entry_wait(mm, pmd, address); goto out; } - delayacct_set_flag(DELAYACCT_PF_SWAPIN); page = lookup_swap_cache(entry); if (!page) { grab_swap_token(); /* Contend for token _before_ read-in */ @@ -2172,7 +2171,6 @@ static int do_swap_page(struct mm_struct page_table = pte_offset_map_lock(mm, pmd, address, &ptl); if (likely(pte_same(*page_table, orig_pte))) ret = VM_FAULT_OOM; - delayacct_clear_flag(DELAYACCT_PF_SWAPIN); goto unlock; } @@ -2181,9 +2179,10 @@ static int do_swap_page(struct mm_struct count_vm_event(PGMAJFAULT); } - delayacct_clear_flag(DELAYACCT_PF_SWAPIN); mark_page_accessed(page); + delayacct_set_flag(DELAYACCT_PF_SWAPIN); lock_page(page); + delayacct_clear_flag(DELAYACCT_PF_SWAPIN); /* * Back out if somebody else already faulted in this pte. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org