linux-kernel - Re: [PATCH v2 1/2] mm: Uncharge poisoned pages

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Date:   Wed, 26 Apr 2017 13:45:00 +1000
From:   Balbir Singh <bsingharora@...il.com>
To:     Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:     Laurent Dufour <ldufour@...ux.vnet.ibm.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 1/2] mm: Uncharge poisoned pages

> > >  static int delete_from_lru_cache(struct page *p)
> > >  {
> > > +	if (memcg_kmem_enabled())
> > > +		memcg_kmem_uncharge(p, 0);
> > > +
> > 
> > The changelog is not quite clear, so we are uncharging a page using
> > memcg_kmem_uncharge for a page in swap cache/page cache?
> 
> Hi Balbir,
> 
> Yes, in the normal page lifecycle, uncharge is done in page free time.
> But in memory error handling case, in-use pages (i.e. swap cache and page
> cache) are removed from normal path and they don't pass page freeing code.
> So I think that this change is to keep the consistent charging for such a case.

I agree we should uncharge, but looking at the API name, it seems to
be for kmem pages, why are we not using mem_cgroup_uncharge()? Am I missing
something?

Balbir Singh.