Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [patch v2 for-4.20] Revert "mm, thp: consolidate THP gfp handling
 into alloc_hugepage_direct_gfpmask"
To:     David Rientjes <rientjes@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Andrea Arcangeli <aarcange@redhat.com>,
        mgorman@techsingularity.net, Michal Hocko <mhocko@kernel.org>,
        ying.huang@intel.com, s.priebe@profihost.ag,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        alex.williamson@redhat.com, lkp@01.org, kirill@shutemov.name,
        Andrew Morton <akpm@linux-foundation.org>,
        zi.yan@cs.rutgers.edu
References: <alpine.DEB.2.21.1812071449500.173448@chino.kir.corp.google.com>
From:   Vlastimil Babka <vbabka@suse.cz>
Openpgp: preference=signencrypt
Autocrypt: addr=vbabka@suse.cz; prefer-encrypt=mutual; keydata=
 xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB
 KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB
 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+
 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy
 tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD
 Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4
 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc
 LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x
 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv
 BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSFWbGFzdGltaWwg
 QmFia2EgPHZiYWJrYUBzdXNlLmNvbT7CwZcEEwEKAEECGwMFCwkIBwMFFQoJCAsFFgIDAQAC
 HgECF4ACGQEWIQSpQNQ0mSwujpkQPVAiT6fnzIKmZAUCWi/zTwUJBbOLuQAKCRAiT6fnzIKm
 ZIpED/4jRN/6LKZZIT4R2xoou0nJkBGVA3nfb+mUMgi3uwn/zC+o6jjc3ShmP0LQ0cdeuSt/
 t2ytstnuARTFVqZT4/IYzZgBsLM8ODFY5vGfPw00tsZMIfFuVPQX3xs0XgLEHw7/1ZCVyJVr
 mTzYmV3JruwhMdUvIzwoZ/LXjPiEx1MRdUQYHAWwUfsl8lUZeu2QShL3KubR1eH6lUWN2M7t
 VcokLsnGg4LTajZzZfq2NqCKEQMY3JkAmOu/ooPTrfHCJYMF/5dpi8YF1CkQF/PVbnYbPUuh
 dRM0m3NzPtn5DdyfFltJ7fobGR039+zoCo6dFF9fPltwcyLlt1gaItfX5yNbOjX3aJSHY2Vc
 A5T+XAVC2sCwj0lHvgGDz/dTsMM9Ob/6rRJANlJPRWGYk3WVWnbgW8UejCWtn1FkiY/L/4qJ
 UsqkId8NkkVdVAenCcHQmOGjRQYTpe6Cf4aQ4HGNDeWEm3H8Uq9vmHhXXcPLkxBLRbGDSHyq
 vUBVaK+dAwAsXn/5PlGxw1cWtur1ep7RDgG3vVQDhIOpAXAg6HULjcbWpBEFaoH720oyGmO5
 kV+yHciYO3nPzz/CZJzP5Ki7Q1zqBb/U6gib2at5Ycvews+vTueYO+rOb9sfD8BFTK386LUK
 uce7E38owtgo/V2GV4LMWqVOy1xtCB6OAUfnGDU2EM7ATQRbGTU1AQgAn0H6UrFiWcovkh6E
 XVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQLa1PQDUi6j00ChlcR66g9/V0sPIcSutacPKf
 dKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMhFmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCT
 sTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sfbAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZO
 rIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq+aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahK
 tQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4njQARAQABwsF8BBgBCgAmFiEEqUDUNJksLo6Z
 ED1QIk+n58yCpmQFAlsZNTUCGwwFCQPCZwAACgkQIk+n58yCpmQ83g/9Frg1sRMdGPn98zV+
 O2eC3h0p5f/oxxQ8MhG5znwHoW4JDG2TuxfcQuz7X7Dd5JWscjlw4VFJ2DD+IrDAGLHwPhCr
 RyfKalnrbYokvbClM9EuU1oUuh7k+Sg5ECNXEsamW9AiWGCaKWNDdHre3Lf4xl+RJWxghOVW
 RiUdpLA/a3yDvJNVr6rxkDHQ1P24ZZz/VKDyP+6g8aty2aWEU0YFNjI+rqYZb2OppDx6fdma
 YnLDcIfDFnkVlDmpznnGCyEqLLyMS3GH52AH13zMT9L9QYgT303+r6QQpKBIxAwn8Jg8dAlV
 OLhgeHXKr+pOQdFf6iu2sXlUR4MkO/5KWM1K0jFR2ug8Pb3aKOhowVMBT64G0TXhQ/kX4tZ2
 ZF0QZLUCHU3Cigvbu4AWWVMNDEOGD/4sn9OoHxm6J04jLUHFUpFKDcjab4NRNWoHLsuLGjve
 Gdbr2RKO2oJ5qZj81K7os0/5vTAA4qHDP2EETAQcunTn6aPlkUnJ8aw6I1Rwyg7/XsU7gQHF
 IM/cUMuWWm7OUUPtJeR8loxZiZciU7SMvN1/B9ycPMFs/A6EEzyG+2zKryWry8k7G/pcPrFx
 O2PkDPy3YmN1RfpIX2HEmnCEFTTCsKgYORangFu/qOcXvM83N+2viXxG4mjLAMiIml1o2lKV
 cqmP8roqufIAj+Ohhzs=
Message-ID: <4ffce3ba-2a80-4d57-876e-32a6b7eae57f@suse.cz>
Date:   Sat, 8 Dec 2018 11:02:36 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.3.2
MIME-Version: 1.0
In-Reply-To: <alpine.DEB.2.21.1812071449500.173448@chino.kir.corp.google.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 12/7/18 11:50 PM, David Rientjes wrote:
> This reverts commit 89c83fb539f95491be80cdd5158e6f0ce329e317.
> 
> This should have been done as part of 2f0799a0ffc0 ("mm, thp: restore
> node-local hugepage allocations").  The movement of the thp allocation
> policy from alloc_pages_vma() to alloc_hugepage_direct_gfpmask() was
> intended to only set __GFP_THISNODE for mempolicies that are not
> MPOL_BIND whereas the revert could set this regardless of mempolicy.
> 
> While the check for MPOL_BIND between alloc_hugepage_direct_gfpmask()
> and alloc_pages_vma() was racy, that has since been removed since the

I would have expected mmap_sem to prevent the race, as faults have it
locked for read and updating mempolicies for write, IIRC? But didn't
check in detail.

> revert.  What is left is the possibility to use __GFP_THISNODE in
> policy_node() when it is unexpected because the special handling for
> hugepages in alloc_pages_vma()  was removed as part of the consolidation.

Yeah that was a bug.

> Secondly, prior to 89c83fb539f9, alloc_pages_vma() implemented a somewhat 
> different policy for hugepage allocations, which were allocated through 
> alloc_hugepage_vma().  For hugepage allocations, if the allocating 
> process's node is in the set of allowed nodes, allocate with 
> __GFP_THISNODE for that node (for MPOL_PREFERRED, use that node with 
> __GFP_THISNODE instead).  This was changed for shmem_alloc_hugepage() to 
> allow fallback to other nodes in 89c83fb539f9 as it did for new_page() in 
> mm/mempolicy.c which is functionally different behavior and removes the 
> requirement to only allocate hugepages locally.

TBH this slight difference was known and stated in the changelog of
89c83fb539f9 so you could have objected.

> So this commit does a full revert of 89c83fb539f9 instead of the partial
> revert that was done in 2f0799a0ffc0.  The result is the same thp
> allocation policy for 4.20 that was in 4.19.
> 
> Fixes: 89c83fb539f9 ("mm, thp: consolidate THP gfp handling into alloc_hugepage_direct_gfpmask")
> Fixes: 2f0799a0ffc0 ("mm, thp: restore node-local hugepage allocations")
> Signed-off-by: David Rientjes <rientjes@google.com>
> ---
>  This indeed restores the thp allocation policy fully to what it was in
>  4.19 since there is obivously more discussion to be had about how the
>  NUMA aspects of thp allocations should be addressed.  We can do this
>  with a stable 4.20 tree in the background that has the same allocation
>  policy that was in 4.0.

I agree that this is probably the safest option for now so that the next
rc doesn't contain the warning introduced in 2f0799a0ffc0.