Messages in this thread | | | Subject | Re: [GIT PULL v2] Early SLAB fixes for 2.6.31 | From | Pekka Enberg <> | Date | Mon, 15 Jun 2009 17:58:11 +0300 |
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On Mon, 2009-06-15 at 10:55 -0400, Christoph Lameter wrote: > On Sun, 14 Jun 2009, Pekka J Enberg wrote: > > > How about something like this? There should be no extra code in fastpaths > > for production configs with this one. > > Yes something like that would be good. More comments below. > > > index 4d6004c..5e8cea1 100644 > > --- a/mm/slub.c > > +++ b/mm/slub.c > > @@ -1613,6 +1613,8 @@ another_slab: > > deactivate_slab(s, c); > > > > new_slab: > > + gfpflags &= slab_gfp_mask; > > + > > Move the processing of GFP_RECLAIM_MASK etc up to here from new_slab? Then > the flow is also more logical. The flags handling is concentrated in one > spot in the allocator and its more obvious how we handle gfp flags.
Sure. Will fix.
> > @@ -1668,13 +1670,14 @@ static __always_inline void *slab_alloc(struct kmem_cache *s, > > struct kmem_cache_cpu *c; > > unsigned long flags; > > unsigned int objsize; > > + gfp_t real_gfp; > > > > - gfpflags &= slab_gfp_mask; > > + real_gfp = gfpflags & slab_gfp_mask; > > > > - lockdep_trace_alloc(gfpflags); > > - might_sleep_if(gfpflags & __GFP_WAIT); > > + lockdep_trace_alloc(real_gfp); > > + might_sleep_if(real_gfp & __GFP_WAIT); > > > > - if (should_failslab(s->objsize, gfpflags)) > > + if (should_failslab(s->objsize, real_gfp)) > > return NULL; > > > > local_irq_save(flags); > > Dont do it there. Only modify the slow path. > > Look at __might_sleep(). It already has an exception for system_state != > RUNNING. If it still triggers then add to the condition there.
But does this matter? When the debugging options are turned off, there are no users for "real_gfp" and thus GCC optimizes everything away. For debugging configs, the extra cacheline load doesn't matter, does it?
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