Re: [patch 7/8] fdmap v2 - implement sys_socket2

[Eric Dumazet <dada1@cosmosbay.com>]

Davide Libenzi a écrit :
> On Thu, 7 Jun 2007, Eric Dumazet wrote:
> 
>> Davide, are you sure we want FIFO for non sequential allocations ?
>>
>> This tends to use all the fmap slots, and not very cache friendly
>> if an app does a lot of [open(),...,close()] things. We already got a 
>> perf drop because of RCUification of file freeing (FIFO mode instead 
>> of LIFO given by kmalloc()/kfree())
>>
>> If the idea behind this FIFO was security (ie not easy for an app to predict 
>> next glibc file handle), we/glibc might use yet another FD_SECUREMODE flag, 
>> wich ORed with O_NONSEQFD would ask to fdmap_newfd() to take the tail of 
>> fmap->slist, not head.
> 
> Uli, would it be OK to rely only on base randomization and use a LIFO 
> instead? We have base randomization, plus LIFO does not mean strictly 
> sequential like legacy allocator, just more compatc and cache friendly.
> 

I am afraid randomization wont really work if /sbin/init or /bin/bash for 
example uses one (or more) unseq fd :
The 'random base' will be propagated at fork()/exec() time ?