LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Michal Hocko <mhocko@kernel.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: Joel Fernandes <joelaf@google.com>,
	Steven Rostedt <rostedt@goodmis.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>,
	"open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>,
	Vlastimil Babka <vbabka@suse.cz>
Subject: Re: [PATCH v1] kernel/trace:check the val against the available mem
Date: Thu, 5 Apr 2018 17:32:40 +0200
Message-ID: <20180405153240.GO6312@dhcp22.suse.cz> (raw)
In-Reply-To: <20180405151359.GB28128@bombadil.infradead.org>

On Thu 05-04-18 08:13:59, Matthew Wilcox wrote:
> On Thu, Apr 05, 2018 at 04:27:49PM +0200, Michal Hocko wrote:
> > On Thu 05-04-18 07:22:58, Matthew Wilcox wrote:
> > > On Wed, Apr 04, 2018 at 09:12:52PM -0700, Joel Fernandes wrote:
> > > > On Wed, Apr 4, 2018 at 7:58 PM, Matthew Wilcox <willy@infradead.org> wrote:
> > > > > I still don't get why you want RETRY_MAYFAIL.  You know that tries
> > > > > *harder* to allocate memory than plain GFP_KERNEL does, right?  And
> > > > > that seems like the exact opposite of what you want.
> 
> Argh.  The comment confused me.  OK, now I've read the source and
> understand that GFP_KERNEL | __GFP_RETRY_MAYFAIL tries exactly as hard
> as GFP_KERNEL *except* that it won't cause OOM itself.  But any other
> simultaneous GFP_KERNEL allocation without __GFP_RETRY_MAYFAIL will
> cause an OOM.  (And that's why we're having a conversation)

Well, I can udnerstand how this can be confusing. The all confusion
boils down to the small-never-fails semantic we have. So all reclaim
modificators (__GFP_NOFAIL, __GFP_RETRY_MAYFAIL, __GFP_NORETRY) only
modify the _default_ behavior.

> That's a problem because we have places in the kernel that call
> kv[zm]alloc(very_large_size, GFP_KERNEL), and that will turn into vmalloc,
> which will do the exact same thing, only it will trigger OOM all by itself
> (assuming the largest free chunk of address space in the vmalloc area
> is larger than the amount of free memory).

well, hardcoded GFP_KERNEL from vmalloc guts is yet another, ehm,
herritage that you are not so proud of.
 
> I considered an alloc_page_array(), but that doesn't fit well with the
> design of the ring buffer code.  We could have:
> 
> struct page *alloc_page_list_node(int nid, gfp_t gfp_mask, unsigned long nr);
> 
> and link the allocated pages together through page->lru.
> 
> We could also have a GFP flag that says to only succeed if we're further
> above the existing watermark than normal.  __GFP_LOW (==ALLOC_LOW),
> if you like.  That would give us the desired behaviour of trying all of
> the reclaim methods that GFP_KERNEL would, but not being able to exhaust
> all the memory that GFP_KERNEL allocations would take.

Well, I would be really careful with yet another gfp mask. They are so
incredibly hard to define properly and then people kinda tend to screw
your best intentions with their usecases ;)
Failing on low wmark is very close to __GFP_NORETRY or even
__GFP_NOWAIT, btw. So let's try to not overthink this...
-- 
Michal Hocko
SUSE Labs

  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
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 [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20180405153240.GO6312@dhcp22.suse.cz \
    --to=mhocko@kernel.org \
    --cc=akpm@linux-foundation.org \
    --cc=huangzhaoyang@gmail.com \
    --cc=joelaf@google.com \
    --cc=kernel-patch-test@lists.linaro.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=mingo@kernel.org \
    --cc=rostedt@goodmis.org \
    --cc=vbabka@suse.cz \
    --cc=willy@infradead.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
	git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git
	git clone --mirror https://lore.kernel.org/lkml/10 lkml/git/10.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git