linux-kernel - Re: [PATCH] fdtable: Eradicate fdarray overflow.

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Message-id: <452DE18B.9030701@cosmosbay.com>
Date:	Thu, 12 Oct 2006 08:32:43 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Vadim Lobanov <vlobanov@...akeasy.net>
Cc:	akpm@...l.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fdtable: Eradicate fdarray overflow.

Vadim Lobanov a écrit :
> On Wednesday 11 October 2006 22:19, Eric Dumazet wrote:
>> Hi Vadim
>>
>> I find your PAGE_SIZE/4 minimum allocation quite unjustified.
>>
>> For architectures with 64K PAGE_SIZE, we endup allocating 16K, for poor
>> tasks that happen to touch a not so high (>= 64) file descriptor...
>>
>> I would vote for a fixed size, like 1024
> 
> In my opinion, always picking 1024 would be highly suboptimal for some 
> architectures (x86-64 in particular -- that's a whole page, just for the 
> fdarray!). If anything, I'd prefer something similar to this pseudo-code:

I was speaking of 1024 bytes.

I was the guy who made fdset going from PAGE_SIZE to 64 bytes (L1_CACHE_BYTES 
if you dare), I wont be the guy responsible for a reverse path on fdtable :)

That is replace your (PAGE_SIZE/4)  by 1024, wich was you probably meant
No archi has a smaller page, so no need to play with min_t() macro...

> 
> #define FDTABLE_MIN min_t(uint, PAGE_SIZE / 4 / sizeof(struct file *), 1024)
> ...
> nr /= FDTABLE_MIN;
> nr = roundup_pow_of_two(nr + 1);
> nr *= FDTABLE_MIN;
> 
> gcc should be smart enough to optimize that expression into a single constant. 
> At least it did (version 4.1.0) in my quick test here.
> 
>> Eric
> 
> Let me know what you think. Please don't just go radio-silent on me. ;)
> 

radio-silent ? well, it seems I already sent you many mails about your patches :)

Eric

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