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SubjectRe: [PATCHv2 2/5] vmscan: Kill hibernation specific reclaim logic and unify it
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On Monday 02 November 2009, KOSAKI Motohiro wrote:
> > > Then, This patch changed shrink_all_memory() to only the wrapper function of
> > > do_try_to_free_pages(). it bring good reviewability and debuggability, and solve
> > > above problems.
> > >
> > > side note: Reclaim logic unificication makes two good side effect.
> > > - Fix recursive reclaim bug on shrink_all_memory().
> > > it did forgot to use PF_MEMALLOC. it mean the system be able to stuck into deadlock.
> > > - Now, shrink_all_memory() got lockdep awareness. it bring good debuggability.
> >
> > As I said previously, I don't really see a reason to keep shrink_all_memory().
> >
> > Do you think that removing it will result in performance degradation?
>
> Hmm...
> Probably, I misunderstood your mention. I thought you suggested to kill
> all hibernation specific reclaim code. I did. It's no performance degression.
> (At least, I didn't observe)
>
> But, if you hope to kill shrink_all_memory() function itsef, the short answer is,
> it's impossible.
>
> Current VM reclaim code need some preparetion to caller, and there are existing in
> both alloc_pages_slowpath() and try_to_free_pages(). We can't omit its preparation.

Well, my grepping for 'shrink_all_memory' throughout the entire kernel source
code seems to indicate that hibernate_preallocate_memory() is the only current
user of it. I may be wrong, but I doubt it, unless some new users have been
added since 2.6.31.

In case I'm not wrong, it should be safe to drop it from
hibernate_preallocate_memory(), because it's there for performance reasons
only. Now, since hibernate_preallocate_memory() appears to be the only user of
it, it should be safe to drop it entirely.

> Please see following shrink_all_memory() code. it's pretty small. it only have
> few vmscan preparation. I don't think it is hard to maintainance.

No, it's not, but I'm really not sure it's worth keeping.

Thanks,
Rafael


> =====================================================
> unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
> {
> struct reclaim_state reclaim_state;
> struct scan_control sc = {
> .gfp_mask = GFP_HIGHUSER_MOVABLE,
> .may_swap = 1,
> .may_unmap = 1,
> .may_writepage = 1,
> .nr_to_reclaim = nr_to_reclaim,
> .hibernation_mode = 1,
> .swappiness = vm_swappiness,
> .order = 0,
> .isolate_pages = isolate_pages_global,
> };
> struct zonelist * zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
> struct task_struct *p = current;
> unsigned long nr_reclaimed;
>
> p->flags |= PF_MEMALLOC;
> lockdep_set_current_reclaim_state(sc.gfp_mask);
> reclaim_state.reclaimed_slab = 0;
> p->reclaim_state = &reclaim_state;
>
> nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
>
> p->reclaim_state = NULL;
> lockdep_clear_current_reclaim_state();
> p->flags &= ~PF_MEMALLOC;
>
> return nr_reclaimed;
> }


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