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Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1raG5Q-0000000Gn3y-2ZrO; Wed, 14 Feb 2024 14:18:08 +0000 Date: Wed, 14 Feb 2024 14:18:08 +0000 From: Matthew Wilcox To: Charan Teja Kalla Cc: David Hildenbrand , gregkh@linuxfoundation.org, akpm@linux-foundation.org, vbabka@suse.cz, dhowells@redhat.com, surenb@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, # see patch description Subject: Re: [PATCH] mm/huge_memory: fix swap entry values of tail pages of THP Message-ID: References: <1707814102-22682-1-git-send-email-quic_charante@quicinc.com> <8620c1a0-e091-46e9-418a-db66e621b9c4@quicinc.com> <845ca78f-913b-4a92-8b40-ff772a7ad333@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Stat-Signature: bei5newrndk9r5hbih6ddzafeeuzde4t X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 11BFE180021 X-Rspam-User: X-HE-Tag: 1707920296-65626 X-HE-Meta: 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 qxKf1k4a cHTZwOCeLzu0LXPDhHj9HH43mGhFgmfpF9LyungfUMW+DStN1lP/RrsfzVTrHgFjVLmgjxQ5MRt5i4dQiO/AYEog2T9qejXvPCEesdHxDwa3cXcputc649bddrluxvuqP7JmrgSVOTjJCoUoP0lcKWpW+4vV4RG77W2q2zRx1ssgL4AbRyiCT/9QQiJJIuf2tw5BPmQA3wl9Im4F0fw74jOtO9Yz5S3g6Lwx24zVfX6G4zKLVRzn3lz4TqQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Feb 14, 2024 at 12:04:10PM +0530, Charan Teja Kalla wrote: > > 1) Is it broken in 5.15? Did you actually try to reproduce or is this > >    just a guess? > > > > We didn't run the tests with THP enabled on 5.15, __so we didn't > encounter this issue__ on older to 6.1 kernels. > > I mentioned that issue exists is based on my understanding after code > walk through. To be specific, I just looked to the > migrate_pages()->..->migrate_page_move_mapping() & > __split_huge_page_tail() where the ->private field of thp sub-pages is > not filled with swap entry. If it could have set, I think these are the > only places where it would have done, per my understanding. CMIW. I think you have a misunderstanding. David's patch cfeed8ffe55b (part of 6.6) _stopped_ us using the tail ->private entries. So in 6.1, these tail pages should already have page->private set, and I don't understand what you're fixing. > > 2) How did you come up with 417013e0d18 ("mm/migrate: Add > >    folio_migrate_mapping()") > OOPS, I mean it is Fixes: 3417013e0d18 ("mm/migrate: Add > folio_migrate_mapping()"). > > My understanding is that it a miss in folio_migrate_mapping() where the > sub-pages should've the ->private set. But this is just a > reimplementation of migrate_page_move_mapping()(where also the issue > exists, tmk). > > commit 3417013e0d183be9b42d794082eec0ec1c5b5f15 > Author: Matthew Wilcox (Oracle) > Date: Fri May 7 07:28:40 2021 -0400 > > mm/migrate: Add folio_migrate_mapping() > > Reimplement migrate_page_move_mapping() as a wrapper around > folio_migrate_mapping(). Saves 193 bytes of kernel text. > > Thanks. >