Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Tue, 30 Jun 2020 08:42:56 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Joonsoo Kim <js1304@gmail.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>, kernel-team@lge.com,
        Vlastimil Babka <vbabka@suse.cz>,
        Christoph Hellwig <hch@infradead.org>,
        Roman Gushchin <guro@fb.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>
Subject: Re: [PATCH v3 4/8] mm/hugetlb: make hugetlb migration callback CMA
 aware
Message-ID: <20200630064256.GB2369@dhcp22.suse.cz>
References: <1592892828-1934-1-git-send-email-iamjoonsoo.kim@lge.com>
 <1592892828-1934-5-git-send-email-iamjoonsoo.kim@lge.com>
 <20200625115422.GE1320@dhcp22.suse.cz>
 <CAAmzW4MHuRhNqVXMntLAc_x4kJgkgQ-pD5GfFxRxJRchrEFr9g@mail.gmail.com>
 <20200626072324.GT1320@dhcp22.suse.cz>
 <CAAmzW4NLVwvqtoUb+JJ+WV=7_n800vA+YYC0LyrDS6iQ7wxcdg@mail.gmail.com>
 <20200629075510.GA32461@dhcp22.suse.cz>
 <CAAmzW4PFEEs0FGe+XMHzRdXr0LpdF3TZZG2L3E+opRyZWDZ48A@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <CAAmzW4PFEEs0FGe+XMHzRdXr0LpdF3TZZG2L3E+opRyZWDZ48A@mail.gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue 30-06-20 15:30:04, Joonsoo Kim wrote:
> 2020년 6월 29일 (월) 오후 4:55, Michal Hocko <mhocko@kernel.org>님이 작성:
[...]
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index 57ece74e3aae..c1595b1d36f3 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -1092,10 +1092,14 @@ static struct page *dequeue_huge_page_nodemask(struct hstate *h, gfp_t gfp_mask,
> >  /* Movability of hugepages depends on migration support. */
> >  static inline gfp_t htlb_alloc_mask(struct hstate *h)
> >  {
> > +       gfp_t gfp;
> > +
> >         if (hugepage_movable_supported(h))
> > -               return GFP_HIGHUSER_MOVABLE;
> > +               gfp = GFP_HIGHUSER_MOVABLE;
> >         else
> > -               return GFP_HIGHUSER;
> > +               gfp = GFP_HIGHUSER;
> > +
> > +       return current_gfp_context(gfp);
> >  }
> >
> >  static struct page *dequeue_huge_page_vma(struct hstate *h,
> >
> > If we even fix this general issue for other allocations and allow a
> > better CMA exclusion then it would be implemented consistently for
> > everybody.
> 
> Yes, I have reviewed the memalloc_nocma_{} APIs and found the better way
> for CMA exclusion. I will do it after this patch is finished.
> 
> > Does this make more sense to you are we still not on the same page wrt
> > to the actual problem?
> 
> Yes, but we have different opinions about it. As said above, I will make
> a patch for better CMA exclusion after this patchset. It will make
> code consistent.
> I'd really appreciate it if you wait until then.

As I've said I would _prefer_ simplicity over "correctness" if it is only
partial and hard to reason about from the userspace experience but this
is not something I would _insist_ on. If Mike as a maintainer of the
code is ok with that then I will not stand in the way.

But please note that a missing current_gfp_context inside
htlb_alloc_mask is a subtle bug. I do not think it matters right now but
with a growing use of scoped apis this might actually hit some day so I
believe we want to have it in place.

Thanks!

-- 
Michal Hocko
SUSE Labs