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Re: rhashtable: Use __vmalloc with GFP_ATOMIC for table allocation

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On Fri, Dec 04, 2015 at 04:53:34PM -0500, David Miller wrote:
> From: Herbert Xu <herbert@gondor.apana.org.au>
> Date: Fri, 4 Dec 2015 22:39:56 +0800
> 
> > When an rhashtable user pounds rhashtable hard with back-to-back
> > insertions we may end up growing the table in GFP_ATOMIC context.
> > Unfortunately when the table reaches a certain size this often
> > fails because we don't have enough physically contiguous pages
> > to hold the new table.
> > 
> > Eric Dumazet suggested (and in fact wrote this patch) using
> > __vmalloc instead which can be used in GFP_ATOMIC context.
> > 
> > Reported-by: Phil Sutter <phil@nwl.cc>
> > Suggested-by: Eric Dumazet <eric.dumazet@gmail.com>
> > Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
> 
> Applied, thanks Herbert.

Sorry Dave but you'll have to revert this because I've been able
to trigger the following crash with the patch:

Testing concurrent rhashtable access from 50 threads
------------[ cut here ]------------
kernel BUG at ../mm/vmalloc.c:1337!
invalid opcode: 0000 [#1] PREEMPT SMP 

The reason is that because I was testing insertions with BH disabled,
and __vmalloc doesn't like that, even with GFP_ATOMIC.  As we
obviously want to continue to support rhashtable users inserting
entries with BH disabled, we'll have to look for an alternate
solution.

Thanks,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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Thread

rhashtable: ENOMEM errors when hit with a flood of insertions Herbert Xu <herbert@gondor.apana.org.au> - 2015-12-03 14:00 +0100
  RE: rhashtable: ENOMEM errors when hit with a flood of insertions David Laight <David.Laight@ACULAB.COM> - 2015-12-03 16:20 +0100
  Re: rhashtable: ENOMEM errors when hit with a flood of insertions Eric Dumazet <eric.dumazet@gmail.com> - 2015-12-03 17:10 +0100
    Re: rhashtable: ENOMEM errors when hit with a flood of insertions Herbert Xu <herbert@gondor.apana.org.au> - 2015-12-04 01:10 +0100
    rhashtable: Use __vmalloc with GFP_ATOMIC for table allocation Herbert Xu <herbert@gondor.apana.org.au> - 2015-12-04 15:50 +0100
      Re: rhashtable: Use __vmalloc with GFP_ATOMIC for table allocation Eric Dumazet <eric.dumazet@gmail.com> - 2015-12-04 18:50 +0100
        Re: rhashtable: Use __vmalloc with GFP_ATOMIC for table allocation Phil Sutter <phil@nwl.cc> - 2015-12-04 19:20 +0100
          Re: rhashtable: Use __vmalloc with GFP_ATOMIC for table allocation Herbert Xu <herbert@gondor.apana.org.au> - 2015-12-05 08:10 +0100
            Re: rhashtable: Use __vmalloc with GFP_ATOMIC for table allocation Thomas Graf <tgraf@suug.ch> - 2015-12-07 16:40 +0100
              Re: rhashtable: Use __vmalloc with GFP_ATOMIC for table allocation David Miller <davem@davemloft.net> - 2015-12-07 20:40 +0100
                Re: rhashtable: Use __vmalloc with GFP_ATOMIC for table allocation Thomas Graf <tgraf@suug.ch> - 2015-12-09 03:20 +0100
                Re: rhashtable: Use __vmalloc with GFP_ATOMIC for table allocation Herbert Xu <herbert@gondor.apana.org.au> - 2015-12-09 03:30 +0100
                Re: rhashtable: Use __vmalloc with GFP_ATOMIC for table allocation Herbert Xu <herbert@gondor.apana.org.au> - 2015-12-09 03:40 +0100
                Re: rhashtable: Use __vmalloc with GFP_ATOMIC for table allocation Thomas Graf <tgraf@suug.ch> - 2015-12-09 03:50 +0100
                Re: rhashtable: Use __vmalloc with GFP_ATOMIC for table allocation Thomas Graf <tgraf@suug.ch> - 2015-12-09 03:40 +0100
      Re: rhashtable: Use __vmalloc with GFP_ATOMIC for table allocation David Miller <davem@davemloft.net> - 2015-12-04 23:00 +0100
        Re: rhashtable: Use __vmalloc with GFP_ATOMIC for table allocation Herbert Xu <herbert@gondor.apana.org.au> - 2015-12-05 08:10 +0100
          Re: rhashtable: Use __vmalloc with GFP_ATOMIC for table allocation David Miller <davem@davemloft.net> - 2015-12-06 04:50 +0100

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