From mboxrd@z Thu Jan 1 00:00:00 1970 From: Glauber Costa Subject: Re: [PATCH] introduce res_counter_charge_nofail() for socket allocations Date: Thu, 19 Jan 2012 16:51:16 +0400 Message-ID: <4F1811C4.50204@parallels.com> References: <1326899758-9013-1-git-send-email-glommer@parallels.com> <20120119124841.GL24386@cmpxchg.org> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20120119124841.GL24386-druUgvl0LCNAfugRpC6u6w@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Johannes Weiner Cc: cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, KAMEZAWA Hiroyuki , Michal Hocko On 01/19/2012 04:48 PM, Johannes Weiner wrote: > On Wed, Jan 18, 2012 at 07:15:58PM +0400, Glauber Costa wrote: >> There is a case in __sk_mem_schedule(), where an allocation >> is beyond the maximum, but yet we are allowed to proceed. >> It happens under the following condition: >> >> sk->sk_wmem_queued + size>= sk->sk_sndbuf >> >> The network code won't revert the allocation in this case, >> meaning that at some point later it'll try to do it. Since >> this is never communicated to the underlying res_counter >> code, there is an inbalance in res_counter uncharge operation. >> >> I see two ways of fixing this: >> >> 1) storing the information about those allocations somewhere >> in memcg, and then deducting from that first, before >> we start draining the res_counter, >> 2) providing a slightly different allocation function for >> the res_counter, that matches the original behavior of >> the network code more closely. >> >> I decided to go for #2 here, believing it to be more elegant, >> since #1 would require us to do basically that, but in a more >> obscure way. >> >> I will eventually submit it through Dave for the -net tree, >> but I wanted to query you guys first, to see if this approach >> is acceptable or if you'd prefer me to try something else. >> >> Thanks >> >> Signed-off-by: Glauber Costa >> Cc: KAMEZAWA Hiroyuki >> Cc: Johannes Weiner >> Cc: Michal Hocko >> --- >> include/linux/res_counter.h | 6 ++++++ >> include/net/sock.h | 10 ++++------ >> kernel/res_counter.c | 25 +++++++++++++++++++++++++ >> net/core/sock.c | 4 ++-- >> 4 files changed, 37 insertions(+), 8 deletions(-) >> >> diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h >> index c9d625c..32a7b02 100644 >> --- a/include/linux/res_counter.h >> +++ b/include/linux/res_counter.h >> @@ -109,12 +109,18 @@ void res_counter_init(struct res_counter *counter, struct res_counter *parent); >> * >> * returns 0 on success and<0 if the counter->usage will exceed the >> * counter->limit _locked call expects the counter->lock to be taken >> + * >> + * charge_nofail works the same, except that it charges the resource >> + * counter unconditionally, and returns< 0 if the after the current >> + * charge we are over limit. >> */ > > res_counter_margin() assumes usage<= limit is always true. Just make > sure you return 0 if that is not the case, or the charge path can get > confused, thinking there is enough room and retry needlessly. > > Otherwise, looks good. You mean return zero in res_counter_charge_fail() if we exceeded the limit? I do that, since one needs to know the allocation was supposed to fail. Or are you talking about something else ?