Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads

From	Phil Sutter <phil@nwl.cc>
Newsgroups	linux.kernel
Subject	Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads
Date	2015-09-01 15:50 +0200
Message-ID	<q3U6K-8ac-29@gated-at.bofh.it> (permalink)
References	(1 earlier) <q35xg-2u8-5@gated-at.bofh.it> <q3v8m-5TL-15@gated-at.bofh.it> <q3SeC-5tT-15@gated-at.bofh.it> <q3TaF-6OS-21@gated-at.bofh.it> <q3Tu3-7qR-11@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Tue, Sep 01, 2015 at 09:00:57PM +0800, Herbert Xu wrote:
> On Tue, Sep 01, 2015 at 02:46:48PM +0200, Phil Sutter wrote:
> >
> > This is not an inherent behaviour of the implementation but general
> > agreement. The insertion may fail non-permanently (returning -EBUSY),
> > users are expected to handle this by retrying the operation.
> 
> Absolutely not.  The only reason for an insertion to fail is if we
> can't allocate enough memory.  Unless the user is also looping its
> kmalloc calls it definitely shouldn't be retrying the insert.

rhashtable_insert_fast() returns -EBUSY if the table is full
(rht_grow_above_100() returns true) and an asynchronous rehash operation
is active. AFAICT, this is not necessarily caused by memory pressure.

> If an expansion fails it means either that the system is suffering
> a catastrophic memory shortage, or the user of rhashtable is doing
> something wrong.

Hmm. Since memory allocation is first tried with GFP_ATOMIC set and upon
failure retried in background, this seems like a situation which might
happen during normal use. If that already indicates a severe problem,
why retry in background at all?

Cheers, Phil
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Thread

[PATCH 1/3] rhashtable-test: add cond_resched() to thread test Phil Sutter <phil@nwl.cc> - 2015-08-28 12:30 +0200
  [PATCH 2/3] rhashtable-test: retry insert operations in threads Phil Sutter <phil@nwl.cc> - 2015-08-28 12:30 +0200
    Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads Thomas Graf <tgraf@suug.ch> - 2015-08-28 13:10 +0200
      Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads Phil Sutter <phil@nwl.cc> - 2015-08-28 13:20 +0200
        Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads Phil Sutter <phil@nwl.cc> - 2015-08-28 15:40 +0200
          Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads Thomas Graf <tgraf@suug.ch> - 2015-08-29 00:50 +0200
            Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads Phil Sutter <phil@nwl.cc> - 2015-08-29 11:10 +0200
              Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads Herbert Xu <herbert@gondor.apana.org.au> - 2015-08-30 09:50 +0200
                Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads Phil Sutter <phil@nwl.cc> - 2015-08-31 13:10 +0200
                Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads Herbert Xu <herbert@gondor.apana.org.au> - 2015-09-01 13:50 +0200
                Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads Phil Sutter <phil@nwl.cc> - 2015-09-01 14:50 +0200
                Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads Herbert Xu <herbert@gondor.apana.org.au> - 2015-09-01 15:10 +0200
                Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads Eric Dumazet <eric.dumazet@gmail.com> - 2015-09-01 15:50 +0200
                Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads Phil Sutter <phil@nwl.cc> - 2015-09-01 15:50 +0200
                Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads Herbert Xu <herbert@gondor.apana.org.au> - 2015-09-01 16:00 +0200
                Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads Phil Sutter <phil@nwl.cc> - 2015-09-01 16:00 +0200
                Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads Herbert Xu <herbert@gondor.apana.org.au> - 2015-09-01 16:10 +0200
                Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads Thomas Graf <tgraf@suug.ch> - 2015-09-01 16:20 +0200
                Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads Herbert Xu <herbert@gondor.apana.org.au> - 2015-09-01 16:20 +0200
                Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads Thomas Graf <tgraf@suug.ch> - 2015-09-01 17:00 +0200
                Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads Herbert Xu <herbert@gondor.apana.org.au> - 2015-09-02 04:10 +0200
                Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads Thomas Graf <tgraf@suug.ch> - 2015-09-02 09:10 +0200
  [PATCH 3/3] rhashtable-test: calculate max_entries value by default Phil Sutter <phil@nwl.cc> - 2015-08-28 12:30 +0200
    Re: [PATCH 3/3] rhashtable-test: calculate max_entries value by  default Thomas Graf <tgraf@suug.ch> - 2015-08-28 13:20 +0200
  Re: [PATCH 1/3] rhashtable-test: add cond_resched() to thread test Thomas Graf <tgraf@suug.ch> - 2015-08-28 13:10 +0200

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