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b=kxiFCM4MJcV/aLWLoH1cJ+nt7/RWWggSenk4fFCmjRqKAZvgCy7+6/imKq1vuaUOE e8AI9PjAWmFo/yrZNICWmQFM0rhdX3q6BmQmeLX6tCbZD5/CDvzLwx4Qtf+8AXohYZ ZJ/leLAdu9nmSxyrDHOYm5IlNEYT57BUVCFlLgEz7Ts5sSOUjLNgk6pnhXhtMCleKB X/Iv/EcFF3b3RhUbEzp3nu+PWRFKOwsWnIS9Ohxt7SNKVXo3f8chZrVW/PWujOfnE5 dKRmaBKTuZtosYuBj6dW4Xj4Xv/UbpCfEYtjuaYRzrXhtYxPDnlNzWh9w5gXbRRZWT 4Jy3to8iIkHgA== Message-ID: <969cb14b-5b8b-48e6-add6-4dd13101dd89@kernel.org> Date: Wed, 17 Jun 2026 20:52:26 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 1/3] mm/compaction: skip isolate mlocked folios when compact_unevictable_allowed=0 Content-Language: en-US To: Wandun Chen , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev Cc: akpm@linux-foundation.org, surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, david@kernel.org, ljs@kernel.org, liam@infradead.org, rppt@kernel.org, bigeasy@linutronix.de, clrkwllms@kernel.org, Alexander.Krabler@kuka.com, Hugh Dickins References: <20260604023812.3700316-1-chenwandun1@gmail.com> <20260604023812.3700316-2-chenwandun1@gmail.com> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam07 X-Rspam-User: X-Stat-Signature: 39bkd1s9winmkzri3dh19am1egepx586 X-Rspamd-Queue-Id: 12E621C000E X-HE-Tag: 1781722352-879928 X-HE-Meta: U2FsdGVkX1/dhqjGmwfoHqphTPrY3zJrq6F7t92/YcsrcLvt1V0n1BuJpt4OctVeBzuji15FhpcwC5odpxzMmi44q/RE85eBMCYm6oKKAJSj1TAtABb1IoT4Ka2Kdtk8flV9LWkH4goI/ylEltAAN8O0RIgHLocrZF352iJvpYGUmhEuP0K0tp7VmNwp/Ah7PUWZDZ4ZEpHiEB3mFDiRGbgOhE0oOvJXWCAHqVvflZ9/TEGydMszUN7Gf25qzqKJ2gDRS++O3OWtHwU8ADo00lK57kcIHEkkemloFXnok7yCW2etn+d0rp8XQN1sNOMkZ9+s3odDs00fKZ9MUYCaTNPrduqTYxZ5pQxUXCTA2+eQjpaKnF4iKH5UkZe0DzoZ31fxpn+ky9HLzZCALz6vTHneo2LGgCROPNFFMiORhma58sS5Vg2kDsuIReFG5Pkg1Ku4pkASOI+fvPufDtRBPmw7nrLSDPY940C2EHJeNT+GVMicscKbk7M4K+C/kLmG0XmDgA1UO0L2pvWHdxqgagRqfT1JYxMnKmf7e4QF8xVQPv1iRomad7y+HzB3kbUBspnXcvSLklANv+rrkkLY3j0z8TTzarybGx3FLYZwb6cMBDKLr6HvT4CviIO9Ap84F1CJwJFl4wpDh3N2/+QVoUret5rSKBe/p1pMWFfhFHfhpoVsZAAnf6IQb7SfxRg7dHHpk/DU++4n105MjqWglQw3aGW6UE/6tYs9oiAljqtgDhXoyEHhCYFI308lwYVh/usVOfZuj2k3JMHb28nHW73Ir5Cwco5Vu57OfdOfFva8w04iKDosnfJD15gBoJapPVSSlPa6xb7MxfYqKILToi8JAnP91Y8vGnVZt/okZKsZ97ebigVF4hI7UrPwEjf7ggNoHgpf9uq4n9Nhb/J+zsNO5R/wUJIJWMln1vTf0jq7wWNpdvfhG8rVjyjJ7j9hnPeW7BeJk7m2n7RcT9z QXnaQr/W 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/4/26 04:38, Wandun Chen wrote: > From: Wandun Chen > > compact_unevictable_allowed is default 0 under PREEMPT_RT, > isolate_migratepages_block() skips folios with PG_unevictable set. > However, mlock_folio() sets PG_mlocked immediately but defers > PG_unevictable to mlock_folio_batch(), result in a folio with > PG_mlocked=1 but PG_unevictable=0. Compaction will isolate such a > folio. > > Fix by checking folio_test_mlocked() together with the existing > folio_test_unevictable() check. > > A similar issue has been reported by Alexander Krabler on a 6.12-rt > aarch64 system. Vlastimil suggested to check the mlocked flag [1]. > > Reported-by: Alexander Krabler > Closes: https://lore.kernel.org/all/DU0PR01MB10385345F7153F334100981888259A@DU0PR01MB10385.eurprd01.prod.exchangelabs.com/ > Suggested-by: Vlastimil Babka > Signed-off-by: Wandun Chen > Link: https://lore.kernel.org/all/33275585-f2db-4779-89f0-3ae24b455a67@suse.cz/ [1] Well in that thread, Hugh doubted my suggestion and then it seems we didn't concluded anything. Did you actually in practice observe the issue that Alexander had, and that this patch fixed it, or is that theoretical? > --- > mm/compaction.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index b776f35ad020..7e07b792bcb5 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -1116,7 +1116,8 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > is_unevictable = folio_test_unevictable(folio); > > /* Compaction might skip unevictable pages but CMA takes them */ > - if (!(mode & ISOLATE_UNEVICTABLE) && is_unevictable) > + if (!(mode & ISOLATE_UNEVICTABLE) && > + (is_unevictable || folio_test_mlocked(folio))) > goto isolate_fail_put; > > /*