Re: [PATCHv2 2/5] vmscan: Kill hibernation specific reclaim logic and unify it

From: KOSAKI Motohiro
Date: Mon Nov 02 2009 - 10:36:25 EST

> > 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?

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.

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.

unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
struct reclaim_state reclaim_state;
struct scan_control sc = {
.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;
reclaim_state.reclaimed_slab = 0;
p->reclaim_state = &reclaim_state;

nr_reclaimed = do_try_to_free_pages(zonelist, &sc);

p->reclaim_state = NULL;
p->flags &= ~PF_MEMALLOC;

return nr_reclaimed;

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