Messages in this thread | | | Date | Wed, 6 Sep 2006 19:21:35 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 8/18] 2.6.17.9 perfmon2 patch for review: event sets and multiplexing support |
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On Wed, 6 Sep 2006 07:50:31 -0700 Stephane Eranian <eranian@hpl.hp.com> wrote:
> > > + > > > + cachep = ctx->flags.mapset ? pfm_set_cachep : pfm_lg_set_cachep; > > > + > > > + new_set = kmem_cache_alloc(cachep, SLAB_ATOMIC); > > > > SLAB_ATOMIC is unreliable. Is it possible to use SLAB_KERNEL here? If > > coms ecallers can sleep and others cannot then passing in the gfp_flags > > would permit improvement here. > > > > I made some changes and now I know I execute this part of the function > with interrupts disabled, holding only the perfmon context lock. I assume > SLAB_KERNEL means, we can sleep. I think I can make this change safely. > > > > > > > + if (ctx->flags.mapset) { > > > + view_size = PAGE_ALIGN(sizeof(struct pfm_set_view)); > > > + view = vmalloc(view_size); > > > > vmalloc() sleeps, so this _could_ have used SLAB_ATOMIC. > > > > I am not sure I follow you here. Are you talking about eh kmem_cache_alloc() > above? >
My logic was as follows:
a) vmalloc() can sleep
b) Stephane at some time tested this conde with CONFIG_DEBUG_SPINLOCK_SLEEP and didn't get sleep-while-atomic warnings out of that vmalloc().
c) Hence this code is never called under spinlock, or with local interrupts disabled.
d) Hence it is safe to convert the earlier SLAB_ATOMIC into SLAB_KERNEL.
If b) is false then it's the vmalloc() call which is incorrect, not the SLAB_ATOMIC.
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