linux-kernel - Re: Linux 4.9-rc6

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Date:   Mon, 21 Nov 2016 05:32:45 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux 4.9-rc6

On Mon, 2016-11-21 at 00:34 -0800, David Rientjes wrote:
> On Sun, 20 Nov 2016, Eric Dumazet wrote:
> 
> > Another potential issue with CONFIG_VMAP_STACK is that we make no
> > attempt to allocate 4 consecutive pages.
> > 
> > Even if we have plenty of memory, 4 calls to alloc_page() are likely to
> > give us 4 pages in completely different locations.
> > 
> > Here I printed the hugepage number of the 4 pages for some stacks :
> > 
> > 
> > 0xffffc9001a07c000-0xffffc9001a081000   20480 _do_fork+0xe1/0x360 pages=4 vmalloc Hfcac Hfeba Hfec0 Hfc9d N0=4
> > 0xffffc9001a084000-0xffffc9001a089000   20480 _do_fork+0xe1/0x360 pages=4 vmalloc Hfc79 Hfc79 Hfc79 Hfc83 N0=4
> > 0xffffc9001a08c000-0xffffc9001a091000   20480 _do_fork+0xe1/0x360 pages=4 vmalloc Hfc9b Hfe91 Hfebe Hfca2 N0=4
> > 0xffffc9001a094000-0xffffc9001a099000   20480 _do_fork+0xe1/0x360 pages=4 vmalloc Hfcaa Hfcaa Hfca6 Hfebc N0=4
> > 0xffffc9001a09c000-0xffffc9001a0a1000   20480 _do_fork+0xe1/0x360 pages=4 vmalloc Hfe9b Hfe90 Hff09 Hfefb N0=4
> > 0xffffc9001a0a4000-0xffffc9001a0a9000   20480 _do_fork+0xe1/0x360 pages=4 vmalloc Hfe94 Hfe62 Hfea0 Hfe7b N0=4
> > 0xffffc9001a0ac000-0xffffc9001a0b1000   20480 _do_fork+0xe1/0x360 pages=4 vmalloc Hfe78 Hff05 Hff05 Hfc74 N0=4
> > 0xffffc9001a0b4000-0xffffc9001a0b9000   20480 _do_fork+0xe1/0x360 pages=4 vmalloc Hfc9b Hfc9b Hfe83 Hf782 N0=4
> > 0xffffc9001a0bc000-0xffffc9001a0c1000   20480 _do_fork+0xe1/0x360 pages=4 vmalloc Hfe78 Hfe78 Hfc7f Hfc7f N0=4
> > 0xffffc9001a0c4000-0xffffc9001a0c9000   20480 _do_fork+0xe1/0x360 pages=4 vmalloc Hfebe Hfebe Hfe82 Hfe85 N0=4
> > 0xffffc9001a0cc000-0xffffc9001a0d1000   20480 _do_fork+0xe1/0x360 pages=4 vmalloc Hfc6b Hfe62 Hfe62 Hfcaa N0=4
> > 0xffffc9001a0d4000-0xffffc9001a0d9000   20480 _do_fork+0xe1/0x360 pages=4 vmalloc Hfebd Hfebd Hfc92 Hfc92 N0=4
> > 
> > This is a vmalloc() generic issue that is worth fixing now ?
> > 
> > Note this RFC might conflict with NUMA interleave policy.
> > 
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index f2481cb4e6b2..0123e97debb9 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -1602,9 +1602,10 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
> >  				 pgprot_t prot, int node)
> >  {
> >  	struct page **pages;
> > -	unsigned int nr_pages, array_size, i;
> > +	unsigned int nr_pages, array_size, i, j;
> >  	const gfp_t nested_gfp = (gfp_mask & GFP_RECLAIM_MASK) | __GFP_ZERO;
> >  	const gfp_t alloc_mask = gfp_mask | __GFP_NOWARN;
> > +	const gfp_t multi_alloc_mask = (gfp_mask & ~__GFP_DIRECT_RECLAIM) | __GFP_NORETRY;
> >  
> >  	nr_pages = get_vm_area_size(area) >> PAGE_SHIFT;
> >  	array_size = (nr_pages * sizeof(struct page *));
> 
> I think multi_alloc_mask wants to use alloc_mask rather than gfp_mask 
> before clearing the bit, otherwise the failed high-order allocations with 
> no chance to reclaim will spew page allocation failure warnings.  Using 
> __GFP_NORETRY here would be a no-op, but it depends on the implementation 
> so no problems setting it.

Oh, this was definitely my intent of course, thanks for noticing this
typo ;)