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

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Date:	Tue, 3 Nov 2009 00:35:30 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	kosaki.motohiro@...fujitsu.com,
	LKML <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	"linux-mm" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCHv2 2/5] vmscan: Kill hibernation specific reclaim logic and unify it

> > 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.

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 = {
                .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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