linux-kernel - Re: [patch 4/4] ipc: sem optimise simple operations

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Message-ID: <4A81B728.7040200@oracle.com>
Date:	Tue, 11 Aug 2009 11:23:36 -0700
From:	Zach Brown <zach.brown@...cle.com>
To:	Manfred Spraul <manfred@...orfullife.com>
CC:	npiggin@...e.de, Andrew Morton <akpm@...ux-foundation.org>,
	Nadia Derbey <Nadia.Derbey@...l.net>,
	Pierre Peiffer <peifferp@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 4/4] ipc: sem optimise simple operations

Manfred Spraul wrote:
> On 08/11/2009 01:09 PM, npiggin@...e.de wrote:
>> Index: linux-2.6/include/linux/sem.h
>> ===================================================================
>> --- linux-2.6.orig/include/linux/sem.h
>> +++ linux-2.6/include/linux/sem.h
>> @@ -86,6 +86,8 @@ struct task_struct;
>>   struct sem {
>>       int    semval;        /* current value */
>>       int    sempid;        /* pid of last operation */
>> +    struct list_head    negv_pending;
>> +    struct list_head    zero_pending;
>>   };
>>    
> struct sem is increased from 8 to 24 bytes.

And larger still with 64bit pointers.

If it's a problem, this can be scaled back.  You can have pointers to
lists and you can have fewer lists.

Hopefully it won't be a problem, though.  We can close our eyes and
pretend that the size of the semaphore sets scale with the size of the
system and that it's such a relatively small consumer of memory that no
one will notice :).

- z
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