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Tue, 29 Sep 2026 22:06:29 +0000 Received: from offworld (unknown [76.167.199.67]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: dave@stgolabs.net) by pdx1-sub0-mail-a214.dreamhost.com (Postfix) with ESMTPSA id 4hvXM24hD3z4D; Tue, 29 Sep 2026 15:06:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=stgolabs.net; s=dreamhost; t=1790719584; bh=rnXRN2btfBjXlj9+UP5d7AbbpYLkqFmJlBHFxGuZnF4=; h=Date:From:To:Cc:Subject:Content-Type; b=iw4O0UlVuUCtg4I3HvnAX7SEl9beq1gzRb52FqW071b8inV64WZoIEJ19cd/REIb+ LK892wufLNL0knY0d1S+dBO+TNlEU2naQh7cfZpsuIuHaptH2/sn35Y3nvS7YkebE0 uF/0z0PfETllsjo7Y1GaiN42oNdDYM49+p5htjFxXyFhcHqgFQnyJ/SyFBGUEXQzyv K0QbMPUlZn/EAK94NpBlitCNpXU9chOIR+XAjrYzkcrBKSy8+G4ZQtsVyGjjzh6yKl RnXbvd7VHNOJvq+wiIBJ3QoSg3qs8twoJcA2PjJcgAlNRNwG6RQqvIIXAiYGZ3dDpG DJpvI6Ac8OrEg== Date: Tue, 29 Sep 2026 15:06:18 -0700 From: Davidlohr Bueso To: Bharata B Rao Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Jonathan.Cameron@huawei.com, dave.hansen@intel.com, gourry@gourry.net, mgorman@techsingularity.net, mingo@redhat.com, peterz@infradead.org, raghavendra.kt@amd.com, riel@surriel.com, rientjes@google.com, sj@kernel.org, weixugc@google.com, willy@infradead.org, ying.huang@linux.alibaba.com, ziy@nvidia.com, nifan.cxl@gmail.com, xuezhengchu@huawei.com, yiannis@zptcorp.com, akpm@linux-foundation.org, david@kernel.org, byungchul@sk.com, kinseyho@google.com, joshua.hahnjy@gmail.com, yuanchu@google.com, balbirs@nvidia.com, alok.rathore@samsung.com, shivankg@amd.com, donettom@linux.ibm.com Subject: Re: [PATCH v8 1/8] mm: migrate: Allow misplaced migration without VMA Message-ID: <20260929220618.6czpcioqwwg66m7c@offworld> References: <20260728054356.291998-1-bharata@amd.com> <20260728054356.291998-2-bharata@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20260728054356.291998-2-bharata@amd.com> User-Agent: NeoMutt/20220429 X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: A66B940004 X-Rspam-User: X-Stat-Signature: j3kgs1kpkxbdjc8rkrtsj151sojwypu7 X-HE-Tag: 1790719590-517714 X-HE-Meta: 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 rxmqlzy3 SN2VIRJGEklML4W/GDzO/Rd+k2Ux5mwQMwfCpTi09LzqRSB+5BgfEJ7dGA8v76pzegWALaakdl7gFP7F/4kUGF9wN51CBXCfQq65SdRFAajxo3bT19uryjKoZJ5WYijtXom/Rr3Y9rmFqRsW+oPZPUKa7TXKssdq6lZYzMejEub0z5FyJETHNzqPyoedfjd+1DXmKlfwEIkXEnsbIidBRpNgK4GVsMBeFv7HmmvN9ctobEQwz/ADRiHoRA94cnxUwP7vMlFHviWCrwCufJrh1PDBeXePBQACCPCZDv7qEThvfnwV3To4BGKbZ1Q5ceq2fKw5I4DcQyEtKBHm6QhTyoYCPmXtQ86znTHzPa26xF4PfrjpP8ELpy5jyVqL73TgQxtYtrEhCEbVnBi7J7MzEnnjOa8PZJIHu9hxjwuDBeanAi5Zv+ikOeXWcsF1OEyBiqlLcjePy9gnBoIs= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 28 Jul 2026, Bharata B Rao wrote: >We want isolation of misplaced folios to work in contexts >where VMA isn't available, typically when performing migrations >from a kernel thread context. In order to prepare for that, >allow migrate_misplaced_folio_prepare() to be called with >a NULL VMA. > >When migrate_misplaced_folio_prepare() is called with non-NULL >VMA, it will check if the folio is mapped shared and that requires >holding PTL lock. This path isn't taken when the function is >invoked with NULL VMA (migration outside of process context). >Therefore, when VMA == NULL, migrate_misplaced_folio_prepare() >does not require the caller to hold the PTL. > >Signed-off-by: Bharata B Rao Reviewed-by: Davidlohr Bueso