2011/12/20 Hugh Dickins <hughd@xxxxxxxxxx>: > On Mon, 19 Dec 2011, KAMEZAWA Hiroyuki wrote: >> From d620ff605a3a592c2b1de3a046498ce5cd3d3c50 Mon Sep 17 00:00:00 2001 >> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> >> Date: Mon, 19 Dec 2011 16:55:10 +0900 >> Subject: [PATCH 2/2] memcg: reset lru to root_mem_cgroup in special cases. >> >> This patch is a fix for memcg-simplify-lru-handling-by-new-rule.patch >> >> After the patch, all pages which will be onto LRU must have sane >> pc->mem_cgroup. But, in special case, it's not set. >> >> If task->mm is NULL or task is TIF_MEMDIE or fatal_signal_pending(), >> try_charge() is bypassed and the new charge will not be charged. And >> pc->mem_cgroup is unset even if the page will be used/mapped and added >> to LRU. To avoid this, this patch charges such pages to root_mem_cgroup, >> then, pc->mem_cgroup will be handled correctly. >> >> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> >> --- >> mm/memcontrol.c | 2 +- >> 1 files changed, 1 insertions(+), 1 deletions(-) >> >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> index 0d6d21c..9268e8e 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -2324,7 +2324,7 @@ nomem: >> *ptr = NULL; >> return -ENOMEM; >> bypass: >> - *ptr = NULL; >> + *ptr = root_mem_cgroup; >> return 0; >> } >> >> -- > Thank you for review. > I'm dubious about this patch: certainly you have not fully justified it. > I sometimes see panics (in !pc->mem_cgroup check in lru code) when I stops test programs by Ctrl-C or some. That was because of this path. I checked this by adding a debug code to make pc->mem_cgroup = NULL in prep_new_page. > I speak from experience: I did *exactly* the same at "bypass" when > I introduced our mem_cgroup_reset_page(), which corresponds to your > mem_cgroup_reset_owner(); it seemed right to me that a successful > (return 0) call to try_charge() should provide a good *ptr. > ok. > But others (Ying and Greg) pointed out that it changes the semantics > of __mem_cgroup_try_charge() in this case, so you need to justify the > change to all those places which do something like "if (ret || !memcg)" > after calling it. Perhaps it is a good change everywhere, but that's > not obvious, so we chose caution. > > Doesn't it lead to bypass pages being marked as charged to root, so > they don't get charged to the right owner next time they're touched? > Yes. You're right. Hm. So, it seems I should add reset_owner() to the !memcg path rather than here. > In our internal kernel, I restored "bypass" to set *ptr = NULL as > before, but routed those callers that need it to continue on to > __mem_cgroup_commit_charge() when it's NULL, and let that do a > quick little mem_cgroup_reset_page() to root_mem_cgroup for this. > Yes, I'll prepare v2. > But I was growing tired of mem_cgroup_reset_page() when I prepared > the rollup I posted two weeks ago, it adds overhead where we don't > want it, so I found a way to avoid it completely. > Hmm. > What you're doing with mem_cgroup_reset_owner() seems reasonable to > me as a phase to go through (though there's probably more callsites > to be found - sorry to be unhelpfully mysterious about that, but > just because per-memcg-lru-locking needed them doesn't imply that > your patchset needs them), but I expect to (offer a patch to) remove > it later. > Sure. I'm now considering, finally, after removing pc->flags, we'll have chance to merge page_cgroup to struct page. If so, reseting pc->mem_cgroup in prep_new_page() will be a choice. > I am intending to rebase upon your patches, or at least the ones > which akpm has already taken in (I've not studied the pcg flag ones, > more noise than I want at the moment). I'm waiting for those to > appear in a linux-next, disappointed that they weren't in today's. > > (But I'm afraid my patches will then clash with Mel's new lru work.) > > I have been running successfully on several machines with an > approximation to what I expect linux-next to be when it has your > patches in. Ran very stably on two, but one hangs in reclaim after > a few hours, that's high on my list to investigate (you made no > change to vmscan.c, maybe the problem comes from Hannes's earlier > patches, but I hadn't noticed it with those alone). > I saw file caches are not reclaimed at all by force_empty...only once. I'm now digging it. Thank you. -Kame -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href