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    SubjectRe: [GIT PULL v2] Early SLAB fixes for 2.6.31
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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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