Linux-mm Archive on lore.kernel.org
 help / color / Atom feed
From: Michal Hocko <mhocko@kernel.org>
To: "Levin, Alexander (Sasha Levin)" <alexander.levin@verizon.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	John Hubbard <jhubbard@nvidia.com>,
	Andreas Dilger <adilger@dilger.ca>,
	Vlastimil Babka <vbabka@suse.cz>
Subject: Re: [PATCH 1/9] mm: introduce kv[mz]alloc helpers
Date: Fri, 2 Jun 2017 09:50:12 +0200
Message-ID: <20170602075012.GC29840@dhcp22.suse.cz> (raw)
In-Reply-To: <20170602074008.wctxj5il3rqnnpbf@sasha-lappy>

On Fri 02-06-17 07:40:12, Sasha Levin wrote:
> On Fri, Jun 02, 2017 at 09:28:56AM +0200, Michal Hocko wrote:
> > On Fri 02-06-17 07:17:22, Sasha Levin wrote:
> > > On Mon, Mar 06, 2017 at 11:30:24AM +0100, Michal Hocko wrote:
> > > > +void *kvmalloc_node(size_t size, gfp_t flags, int node)
> > > > +{
> > > > +	gfp_t kmalloc_flags = flags;
> > > > +	void *ret;
> > > > +
> > > > +	/*
> > > > +	 * vmalloc uses GFP_KERNEL for some internal allocations (e.g page tables)
> > > > +	 * so the given set of flags has to be compatible.
> > > > +	 */
> > > > +	WARN_ON_ONCE((flags & GFP_KERNEL) != GFP_KERNEL);
> > > 
> > > Hm, there are quite a few locations in the kernel that do something like:
> > > 
> > > 	__vmalloc(len, GFP_NOFS, PAGE_KERNEL);
> > > 
> > > According to your patch, vmalloc can't really do GFP_NOFS, right?
> > 
> > Yes. It is quite likely that they will just work because the hardcoded
> > GFP_KERNEL inside the vmalloc path is in unlikely paths (page table
> > allocations for example) but yes they are broken. I didn't convert some
> > places which opencode the kvmalloc with GFP_NOFS because I strongly
> > _believe_ that the GFP_NOFS should be revisited, checked whether it is
> > needed, documented if so and then memalloc_nofs__{save,restore} be used
> > for the scope which is reclaim recursion unsafe. This would turn all
> > those vmalloc users to the default GFP_KERNEL and still do the right
> > thing.
> 
> While you haven't converted those paths, other folks have picked up
> on that:
> 
> 	commit beeeccca9bebcec386cc31c250cff8a06cf27034
> 	Author: Vinnie Magro <vmagro@fb.com>
> 	Date:   Thu May 25 12:18:02 2017 -0700
> 
> 	    btrfs: Use kvzalloc instead of kzalloc/vmalloc in alloc_bitmap
> 	[...]
> 
> Maybe we should make kvmalloc_node() fail non-GFP_KERNEL allocations
> rather than just warn on them to make this error more evident?

The above has been already discussed [1] and will be dropped with a more
appropriate alternative. I do not think we should be failing those,
though. Supported flags are documented and the warn on will tell that
something is clearly wrong.

>  I'm not sure how these warnings were missed during testing.

I suspect this conversion just hasn't been tested because it is an
"obvious cleanup"

[1] http://lkml.kernel.org/r/20170531063033.GC1795@yexl-desktop

-- 
Michal Hocko
SUSE Labs

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

  reply index

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-06 10:30 [PATCH 0/6 v5] kvmalloc Michal Hocko
2017-03-06 10:30 ` [PATCH 1/9] mm: introduce kv[mz]alloc helpers Michal Hocko
2017-06-02  7:17   ` Levin, Alexander (Sasha Levin)
2017-06-02  7:28     ` Michal Hocko
2017-06-02  7:40       ` Levin, Alexander (Sasha Levin)
2017-06-02  7:50         ` Michal Hocko [this message]
2017-03-06 10:30 ` [PATCH 2/9] mm: support __GFP_REPEAT in kvmalloc_node for >32kB Michal Hocko
2017-04-07  0:45   ` Shakeel Butt
2017-04-07  7:40     ` Michal Hocko
2017-03-06 10:30 ` [PATCH 3/9] rhashtable: simplify a strange allocation pattern Michal Hocko
2017-03-06 10:30 ` [PATCH 4/9] ila: " Michal Hocko
2017-03-06 10:33 ` [PATCH 5/9] xattr: zero out memory copied to userspace in getxattr Michal Hocko
2017-03-06 10:33   ` [PATCH 6/9] treewide: use kv[mz]alloc* rather than opencoded variants Michal Hocko
2017-03-06 10:33   ` [PATCH 7/9] net: use kvmalloc with __GFP_REPEAT rather than open coded variant Michal Hocko
2017-03-30 23:21     ` Shakeel Butt
2017-03-31  8:46       ` Michal Hocko
2017-03-06 10:33   ` [PATCH 8/9] md: use kvmalloc rather than opencoded variant Michal Hocko
2017-03-06 10:33   ` [PATCH 9/9] bcache: use kvmalloc Michal Hocko
  -- strict thread matches above, loose matches on Subject: below --
2017-01-30  9:49 [PATCH 0/6 v3] kvmalloc Michal Hocko
2017-01-30  9:49 ` [PATCH 1/9] mm: introduce kv[mz]alloc helpers Michal Hocko

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=20170602075012.GC29840@dhcp22.suse.cz \
    --to=mhocko@kernel.org \
    --cc=adilger@dilger.ca \
    --cc=akpm@linux-foundation.org \
    --cc=alexander.levin@verizon.com \
    --cc=jhubbard@nvidia.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=vbabka@suse.cz \
    /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

Linux-mm Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-mm/0 linux-mm/git/0.git

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

Example config snippet for mirrors

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


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