linux-kernel - Re: [PATCH v4 1/3] mm/khugepaged: refactor collapse

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Date:   Wed, 22 Feb 2023 11:24:54 -0500
From:   Peter Xu <peterx@...hat.com>
To:     David Stevens <stevensd@...omium.org>
Cc:     linux-mm@...ck.org, Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Yang Shi <shy828301@...il.com>,
        David Hildenbrand <david@...hat.com>,
        Hugh Dickins <hughd@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/3] mm/khugepaged: refactor collapse_file control flow

On Wed, Feb 22, 2023 at 01:08:19PM +0900, David Stevens wrote:
> > >  out:
> > >       VM_BUG_ON(!list_empty(&pagelist));
> > > -     if (hpage) {
> > > -             mem_cgroup_uncharge(page_folio(hpage));
> > > -             put_page(hpage);
> > > -     }
> >
> > Moving this chunk seems wrong, as it can leak the huge page if
> > alloc_charge_hpage() failed on mem charging, iiuc.
> >
> > And I found that keeping it seems wrong either, because if mem charge
> > failed we'll uncharge even without charging it before.  But that's nothing
> > about this patch alone.
> >
> > Posted a patch for this:
> >
> > https://lore.kernel.org/all/20230221214344.609226-1-peterx@redhat.com/

[1]

> >
> > I _think_ this patch will make sense after rebasing to that fix if that's
> > correct, but please review it and double check.
> >
> 
> Ah, good catch. I didn't notice that alloc_charge_hpage could allocate
> *hpage even on failure. The failure path should work properly with
> your fix.

Thanks for confirming.

If we can merge above [1] before this patch, then I think this patch is
correct.  Only if so:

Acked-by: Peter Xu <peterx@...hat.com>

-- 
Peter Xu