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Date: Sat, 13 Dec 2008 09:49:49 +0000 (GMT) From: Hugh Dickins <hugh@...itas.com> To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> cc: Daisuke Nishimura <nishimura@....nes.nec.co.jp>, "linux-mm@...ck.org" <linux-mm@...ck.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>, "akpm@...ux-foundation.org" <akpm@...ux-foundation.org> Subject: Re: [BUGFIX][PATCH mmotm] memcg fix swap accounting leak (v2) On Sat, 13 Dec 2008, KAMEZAWA Hiroyuki wrote: > --- mmotm-2.6.28-Dec12.orig/mm/memory.c > +++ mmotm-2.6.28-Dec12/mm/memory.c > > - mem_cgroup_commit_charge_swapin(page, ptr); > inc_mm_counter(mm, anon_rss); > pte = mk_pte(page, vma->vm_page_prot); > if (write_access && reuse_swap_page(page)) { > pte = maybe_mkwrite(pte_mkdirty(pte), vma); > write_access = 0; > } > - > flush_icache_page(vma, page); > set_pte_at(mm, address, page_table, pte); > page_add_anon_rmap(page, vma, address); > + /* It's better to call commit-charge after rmap is established */ > + mem_cgroup_commit_charge_swapin(page, ptr); > > swap_free(entry); > if (vm_swap_full() || (vma->vm_flags & VM_LOCKED) || PageMlocked(page)) That ordering is back to how it was before I adjusted it for reuse_swap_page()'s delete_from_swap_cache(), isn't it? So I don't understand how you've fixed the bug I hit (not an accounting imbalance but an oops or BUG, I forget) with this ordering, without making some other change elsewhere. mem_cgroup_commit_charge_swapin calls swap_cgroup_record with bogus swp_entry_t 0, which appears to belong to swp_offset 0 of swp_type 0, but the ctrl->map for type 0 may have been freed ages ago (we do always start from 0, but maybe we swapped on type 1 and swapped off type 0 meanwhile). I'm guessing that by looking at the code, not by retesting it, so I may have the details wrong; but I didn't reorder your code just for fun. Perhaps your restored ordering works if you check PageSwapCache in mem_cgroup_commit_charge_swapin or check 0 in swap_cgroup_record, but I don't see that in yesterday's mmotm, nor in this patch. (And I should admit, I've not even attempted to follow your accounting justification: I'll leave that to you memcg guys.) An alternative could be not to clear page->private when deleting from swap cache, that's only done for tidiness and to force notice of races like this; but I'd want a much stronger reason to change that. Or am I making this up? As I say, I've not tested it this time around. Hugh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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