Re: Redundant uses of might_sleep_if()

[Andrew Morton <akpm@osdl.org>]

ioana alexandrescu <ioanamitu@yahoo.com> wrote:
>
> In kernel 2.6.1 it appears that the only necessary
> uses of might_sleep_if()are in __alloc_pages(), and
> perhaps, in cache_alloc_debugcheck_before() (see
> notes).
> 
> Other uses of might_sleep_if() appear to be redundant:
> 
> Pte_chain_alloc()-->might_sleep_if(), but also
> Pte_chain_alloc-->kmem_cache_alloc
>   -->__cache_alloc  -->__cache_alloc()
>   -->cache_alloc_debugcheck_before()
>   -->might_sleep_if()
> 
> skb_share_check()-->might_sleep_if(), but also
> skb_share_check()-->skb_clone()
>   -->kmem_cache_alloc()[as above]
> 
> skb_unshare()-->might_sleep_if(), but also
> skb_unshare()-->skb_copy()
>   -->kmem_cache_alloc()[as above]
> 
> Other paths through skb_unshare, same result.
> 
> 
> QUERY: Should these redundant uses be patched out?

Nope.

Take the case of pte_chain_alloc().  Most of the time, it won't call
kmem_cache_alloc() at all.  But sometimes it will.  But we want to run the
might_sleep() check *every* time someone calls pte_chain_alloc(), not just
some of the times.