netdev - Re: [PATCH 0/6 v3] kvmalloc

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Date:   Thu, 26 Jan 2017 11:32:16 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>, Mel Gorman <mgorman@...e.de>,
        Johannes Weiner <hannes@...xchg.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        marcelo.leitner@...il.com
Subject: Re: [PATCH 0/6 v3] kvmalloc

On Thu 26-01-17 11:08:02, Michal Hocko wrote:
> On Thu 26-01-17 10:36:49, Daniel Borkmann wrote:
> > On 01/26/2017 08:43 AM, Michal Hocko wrote:
> > > On Wed 25-01-17 21:16:42, Daniel Borkmann wrote:
> [...]
> > > > I assume that kvzalloc() is still the same from [1], right? If so, then
> > > > it would unfortunately (partially) reintroduce the issue that was fixed.
> > > > If you look above at flags, they're also passed to __vmalloc() to not
> > > > trigger OOM in these situations I've experienced.
> > > 
> > > Pushing __GFP_NORETRY to __vmalloc doesn't have the effect you might
> > > think it would. It can still trigger the OOM killer becauset the flags
> > > are no propagated all the way down to all allocations requests (e.g.
> > > page tables). This is the same reason why GFP_NOFS is not supported in
> > > vmalloc.
> > 
> > Ok, good to know, is that somewhere clearly documented (like for the
> > case with kmalloc())?
> 
> I am afraid that we really suck on this front. I will add something.

So I have folded the following to the patch 1. It is in line with
kvmalloc and hopefully at least tell more than the current code.
---
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index d89034a393f2..6c1aa2c68887 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1741,6 +1741,13 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
  *	Allocate enough pages to cover @size from the page level
  *	allocator with @gfp_mask flags.  Map them into contiguous
  *	kernel virtual space, using a pagetable protection of @prot.
+ *
+ *	Reclaim modifiers in @gfp_mask - __GFP_NORETRY, __GFP_REPEAT
+ *	and __GFP_NOFAIL are not supported
+ *
+ *	Any use of gfp flags outside of GFP_KERNEL should be consulted
+ *	with mm people.
+ *
  */
 static void *__vmalloc_node(unsigned long size, unsigned long align,
 			    gfp_t gfp_mask, pgprot_t prot,
-- 
Michal Hocko
SUSE Labs