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From: Joel Fernandes <joelaf@google.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Matthew Wilcox <willy@infradead.org>,
	Zhaoyang Huang <huangzhaoyang@gmail.com>,
	Ingo Molnar <mingo@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	kernel-patch-test@lists.linaro.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Michal Hocko <mhocko@suse.com>,
	"open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH v1] kernel/trace:check the val against the available mem
Date: Fri, 30 Mar 2018 16:38:52 -0700
Message-ID: <CAJWu+orx=NZrkAf7x_HqttnrMssmW7DPZOL1fxR=N6D_-fbmtw@mail.gmail.com> (raw)
In-Reply-To: <20180330174209.4cb77003@gandalf.local.home>

Hi Steven,

On Fri, Mar 30, 2018 at 2:42 PM, Steven Rostedt <rostedt@goodmis.org> wrote:
> On Fri, 30 Mar 2018 17:30:31 -0400
> Steven Rostedt <rostedt@goodmis.org> wrote:
>
>> I'll take a look at si_mem_available() that Joel suggested and see if
>> we can make that work.
>
> Wow, this appears to work great! Joel and Zhaoyang, can you test this?
>
> -- Steve
>
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index a2fd3893cc02..32a803626ee2 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -1164,6 +1164,11 @@ static int __rb_allocate_pages(long nr_pages, struct list_head *pages, int cpu)
>         struct buffer_page *bpage, *tmp;
>         long i;
>
> +       /* Check if the available memory is there first */
> +       i = si_mem_available();
> +       if (i < nr_pages)

Does it make sense to add a small margin here so that after ftrace
finishes allocating, we still have some memory left for the system?
But then then we have to define a magic number :-|

> +               return -ENOMEM;
> +

I tested in Qemu with 1GB memory, I am always able to get it to fail
allocation even without this patch without causing an OOM. Maybe I am
not running enough allocations in parallel or something :)

The patch you shared using si_mem_available is working since I'm able
to allocate till the end without a page allocation failure:

bash-4.3# echo 237800 > /d/tracing/buffer_size_kb
bash: echo: write error: Cannot allocate memory
bash-4.3# echo 237700 > /d/tracing/buffer_size_kb
bash-4.3# free -m
             total         used         free       shared      buffers
Mem:           985          977            7           10            0
-/+ buffers:                977            7
Swap:            0            0            0
bash-4.3#

I think this patch is still good to have, since IMO we should not go
and get page allocation failure (even if its a non-OOM) and subsequent
stack dump from mm's allocator, if we can avoid it.

Tested-by: Joel Fernandes <joelaf@google.com>

thanks,

- Joel

  reply index

Thread overview: 64+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-29 10:41 Zhaoyang Huang
2018-03-29 16:05 ` Steven Rostedt
2018-03-30  3:32   ` Zhaoyang Huang
2018-03-30 14:07     ` Steven Rostedt
2018-03-30  6:53 ` [Kernel-patch-test] " kbuild test robot
2018-03-30  6:54 ` kbuild test robot
2018-03-30 14:20 ` Steven Rostedt
2018-03-30 16:37   ` Joel Fernandes
2018-03-30 19:10     ` Steven Rostedt
2018-03-30 20:37       ` Joel Fernandes
2018-03-30 20:53   ` Matthew Wilcox
2018-03-30 21:30     ` Steven Rostedt
2018-03-30 21:42       ` Steven Rostedt
2018-03-30 23:38         ` Joel Fernandes [this message]
2018-03-31  1:41           ` Steven Rostedt
2018-03-31  2:18             ` Matthew Wilcox
2018-03-31  3:07               ` Steven Rostedt
2018-03-31  5:44                 ` Joel Fernandes
2018-04-02  0:52         ` Zhaoyang Huang
2018-04-03 11:06   ` Michal Hocko
2018-04-03 11:51     ` Steven Rostedt
2018-04-03 12:16       ` Michal Hocko
2018-04-03 12:23         ` Steven Rostedt
2018-04-03 12:35           ` Michal Hocko
2018-04-03 13:32             ` Steven Rostedt
2018-04-03 13:56               ` Michal Hocko
2018-04-03 14:17                 ` Steven Rostedt
2018-04-03 16:11                   ` Michal Hocko
2018-04-03 16:59                     ` Steven Rostedt
2018-04-03 22:56                     ` Steven Rostedt
2018-04-04  6:20                       ` Michal Hocko
2018-04-04 12:21                         ` Joel Fernandes
2018-04-04 12:59                         ` Steven Rostedt
2018-04-04 14:10                           ` Michal Hocko
2018-04-04 14:25                             ` Steven Rostedt
2018-04-04 14:42                               ` Michal Hocko
2018-04-04 15:04                                 ` Steven Rostedt
2018-04-04 15:27                                   ` Michal Hocko
2018-04-04 15:38                                     ` Steven Rostedt
2018-04-04  2:58                 ` Zhaoyang Huang
2018-04-04  6:23                   ` Michal Hocko
2018-04-04  9:29                     ` Zhaoyang Huang
2018-04-04 14:11                     ` Steven Rostedt
2018-04-04 14:23                       ` Michal Hocko
2018-04-04 14:31                         ` Steven Rostedt
2018-04-04 14:47                           ` Michal Hocko
2018-04-04 15:47                         ` Steven Rostedt
2018-04-05  2:58                           ` Matthew Wilcox
2018-04-05  4:12                             ` Joel Fernandes
2018-04-05 14:22                               ` Matthew Wilcox
2018-04-05 14:27                                 ` Michal Hocko
2018-04-05 14:34                                   ` Steven Rostedt
2018-04-05 15:13                                   ` Matthew Wilcox
2018-04-05 15:32                                     ` Michal Hocko
2018-04-05 16:15                                       ` Matthew Wilcox
2018-04-05 18:54                                         ` Michal Hocko
2018-04-05 20:15                                           ` __GFP_LOW Matthew Wilcox
2018-04-06  6:09                                             ` __GFP_LOW Michal Hocko
2018-04-08  4:27                                               ` __GFP_LOW Matthew Wilcox
2018-04-09  7:34                                                 ` __GFP_LOW Michal Hocko
2018-04-09 15:51                                                   ` __GFP_LOW Matthew Wilcox
2018-04-09 18:14                                                     ` __GFP_LOW Michal Hocko
     [not found]                                                       ` <CA+JonM0HG9kWb6-0iyDQ8UMxTeR-f=+ZL89t5DvvDULDC8Sfyw@mail.gmail.com>
2018-04-10 12:19                                                         ` __GFP_LOW Matthew Wilcox
2018-04-05 14:30                                 ` [PATCH v1] kernel/trace:check the val against the available mem Steven Rostedt

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