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From:   Shakeel Butt <shakeelb@google.com>
Date:   Thu, 26 May 2022 18:40:18 -0700
Message-ID: <CALvZod7iyO5Ti5xhzq36UjDFNAmfEyPk1MQv_t4kUHKuPCeNng@mail.gmail.com>
Subject: Re: [PATCH] XArray: handle XA_FLAGS_ACCOUNT in xas_split_alloc
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Vasily Averin <vvs@openvz.org>, kernel@openvz.org,
        LKML <linux-kernel@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Johannes Weiner <hannes@cmpxchg.org>
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On Thu, May 26, 2022 at 6:21 PM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Wed, May 25, 2022 at 11:26:37AM +0300, Vasily Averin wrote:
> > Commit 7b785645e8f1 ("mm: fix page cache convergence regression")
> > added support of new XA_FLAGS_ACCOUNT flag into all Xarray allocation
> > functions. Later commit 8fc75643c5e1 ("XArray: add xas_split")
> > introduced xas_split_alloc() but missed about XA_FLAGS_ACCOUNT
> > processing.
>
> Thanks, Vasily.
>
> Johannes, Shakeel, is this right?  I don't fully understand the accounting
> stuff.
>

If called from __filemap_add_folio() then this is correct.

However from split_huge_page_to_list(), we can not use the memcg from
current as that codepath is called from reclaim which can be triggered
by processes of other memcgs.

> > Signed-off-by: Vasily Averin <vvs@openvz.org>
> > ---
> >  lib/xarray.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/lib/xarray.c b/lib/xarray.c
> > index 54e646e8e6ee..5f5b42e6f842 100644
> > --- a/lib/xarray.c
> > +++ b/lib/xarray.c
> > @@ -1013,6 +1013,8 @@ void xas_split_alloc(struct xa_state *xas, void *entry, unsigned int order,
> >       if (xas->xa_shift + XA_CHUNK_SHIFT > order)
> >               return;
> >
> > +     if (xas->xa->xa_flags & XA_FLAGS_ACCOUNT)
> > +             gfp |= __GFP_ACCOUNT;
> >       do {
> >               unsigned int i;
> >               void *sibling = NULL;
> > --
> > 2.31.1
> >