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Thu, 04 Apr 2024 13:48:56 -0700 (PDT) MIME-Version: 1.0 References: <20240404162515.527802-1-fvdl@google.com> <93eccef7-a559-4ad8-be0f-8cc99c00bd09@redhat.com> In-Reply-To: <93eccef7-a559-4ad8-be0f-8cc99c00bd09@redhat.com> From: Frank van der Linden Date: Thu, 4 Apr 2024 13:48:45 -0700 Message-ID: Subject: Re: [PATCH 1/2] mm/cma: drop incorrect alignment check in cma_init_reserved_mem To: David Hildenbrand Cc: linux-mm@kvack.org, muchun.song@linux.dev, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, Marek Szyprowski Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 5B464160011 X-Rspam-User: X-Stat-Signature: mdrhdrwf15iy5p6ou35oize5d1m8ypdk X-Rspamd-Server: rspam03 X-HE-Tag: 1712263738-905363 X-HE-Meta: U2FsdGVkX19pDSuZFJdT6pp98INUa0Wft1OcDAIadiBvKQ44cqzCXZlGrHJnsjUJGfInlDCWh5xfyZfEVOnIP/GflCFvW7b2vkT78/QPaHHvCySQmFzO24JOHNM70ZiTgYuYF0z9dxRcQ1Eo16yQYRWESlAS3ckMyhT1Wing7pdfGxxKMuevSPraNbP7cbKL8GYlbLVmKD61wgRF+7Sdm+lgfqXqwytz5Fk0UVyyEH/lLZOdX6rsNg1fR/pnPmXz0r+Yo7qE5izl4KnFVR9oQQFQnpPx2uYrELk2FPOT/aRYD0p9pyKSfFjwCPDyStnQGutxlZE2NHowOTBeCosaLcHoHwzXgoZvmFUOc4Wq1WQUBNHGhZvQO6h2ErOAfrEuVmeZtWhx7+IzNgqq537baku26iH9Aoer0l2MrMmJeN3gVB6y5EgOb0iOOR/A0PDxfPFlIQDz6WzY/lBC+pxWun1BlCpzR6OLe2yPLh3KtrFRpzydc2donY2iMUQ+mLEDioxbaoDWxeC4IBWD3xPb1W6PSfM6uA2XS0ItoGiVHNSGrYdVjoj3bSl67mxo+nKDWHZ8FZJI1xX/LEaAOmruEak1cnKNsyfeqtGIq8lY5stS1+5Jb3k4uTJiUr2w8z/K5awqgMsRqaaCrsGkCaRIJ3wD4fdx4nwXToB6fWMVpt5N/5o5wNu+rlJ1JturDE+LZbnB4dsXVhJKqCH4fqGH+bcYSueO6XWkblz0stP9bF6iN7wKRZK6hSNZX/mfYLj5oxbf+H6PMWcethRbn3p+Z5vAXYxx0C2a8aVQnXk09T0HidYb6C+1XkeEuU8tp1JGhrTqVICHlpB/Vyw6Lc+XujgwKbRnFmuFIVSXl5ZchDnvLVQk/ZKz4Oa2hea8l0fJnFORoOEeDlxKBjphpHLkChrLGvfcm8qt8lORZMhLHOc22lh3bdV6XOGWzdTiGErFvUvdsRpCzrkQUmQAjAU IprjvA0P inQsw4mC6L+tjDbaB+6COt5TlQhXhZF1WJ0s2WCK3E4o9L103gS8hZgYAZttDzzA9Ijj/mXTsiVNmGW02kpEV0je8siFgrkfF6AvFURJfl8G3R4JBqtqBy+Y54vgJguRM/OqDx3IDpj2rHIKMSywyyMK9q/FCEf/SA61JdyuzR8oTS8IypdLVhPy7DXAxoLEGuLao60E8ALnzOrIeuzSkVJgoYSK0D3O4auYx6bxFenxjxuCdrpDHmye6z4NPA+uwgIMkHP/kCdoAdFFomQkCBVsBOrQu1MhC7HIh/MLE26SUvJxuqBcRiXuxO9KpuXK3pVYitQdmSuV4RwSkZp+JW/jVHw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000060, 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 Thu, Apr 4, 2024 at 1:05=E2=80=AFPM David Hildenbrand = wrote: > > On 04.04.24 18:25, Frank van der Linden wrote: > > cma_init_reserved_mem uses IS_ALIGNED to check if the size > > represented by one bit in the cma allocation bitmask is > > aligned with CMA_MIN_ALIGNMENT_BYTES (pageblock size). > > I recall the important part is that our area always covers full > pageblocks (CMA_MIN_ALIGNMENT_BYTES), because we cannot have "partial > CMA" pageblocks. > > Internally, allocating from multiple pageblock should just work. > > It's late in Germany, hopefully I am not missing something > > Acked-by: David Hildenbrand > > > > > However, this is too strict, as this will fail if > > order_per_bit > pageblock_order, which is a valid configuration. > > > > We could check IS_ALIGNED both ways, but since both numbers are > > powers of two, no check is needed at all. > > > > Signed-off-by: Frank van der Linden > > Cc: Marek Szyprowski > > Cc: David Hildenbrand > > Fixes: de9e14eebf33 ("drivers: dma-contiguous: add initialization from = device tree") > > Is there are real setup/BUG we are fixing? Why did we not stumble over > that earlier? > > If so, please describe that in the patch description. Nobody stumbled over it because the only user of CMA that should have passed in an order_per_bit large enough to trigger this was hugetlb_cma. However, because of a bug, it didn't :) When I fixed that, I noticed that this check fired. - Frank