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Thu, 6 Jun 2024 13:12:00 +1000 (AEST) From: Michael Ellerman To: David Hildenbrand , Yu Zhao , Erhard Furtner Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Subject: Re: kswapd0: page allocation failure: order:0, mode:0x820(GFP_ATOMIC), nodemask=(null),cpuset=/,mems_allowed=0 (Kernel v6.5.9, 32bit ppc) In-Reply-To: <45fc081c-ee8d-4774-a597-708d2924f812@redhat.com> References: <20240508202111.768b7a4d@yea> <20240515224524.1c8befbe@yea> <45fc081c-ee8d-4774-a597-708d2924f812@redhat.com> Date: Thu, 06 Jun 2024 13:11:59 +1000 Message-ID: <87tti6pxxc.fsf@mail.lhotse> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Stat-Signature: b871htupgu8aepeepfjwpa6e5bsdqipa X-Rspamd-Queue-Id: 685921A0008 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1717643524-456230 X-HE-Meta: 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 pZnZPyH6 yR0T/4AGnH+Mby+ujY8CxkpL8iVL5wFcfhj0AxtDXh1GX0BR9aYBhwfBt7GIRMHzVEwQT67XMMg+FL0GTn3e/+ozWLEjNwFMC1S48x2k9C3gDZ35QsayT8pVo70swZeFz+X6fcSBgmUEKTFCAR8DEZqETjbe1AIQh9PSTIIT97R3S3mV1B4F4GjG7yo3klKijxSBY7w2C0fcVw66E0sEHfaBjq+hfPnQutReU 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: David Hildenbrand writes: > On 01.06.24 08:01, Yu Zhao wrote: >> On Wed, May 15, 2024 at 4:06=E2=80=AFPM Yu Zhao wrot= e: ... >>=20 >> Your system has 2GB memory and it uses zswap with zsmalloc (which is >> good since it can allocate from the highmem zone) and zstd/lzo (which >> doesn't matter much). Somehow -- I couldn't figure out why -- it >> splits the 2GB into a 0.25GB DMA zone and a 1.75GB highmem zone: >>=20 >> [ 0.000000] Zone ranges: >> [ 0.000000] DMA [mem 0x0000000000000000-0x000000002fffffff] >> [ 0.000000] Normal empty >> [ 0.000000] HighMem [mem 0x0000000030000000-0x000000007fffffff] > > That's really odd. But we are messing with "PowerMac3,6", so I don't=20 > really know what's right or wrong ... The DMA zone exists because 9739ab7eda45 ("powerpc: enable a 30-bit ZONE_DMA for 32-bit pmac") selects it. It's 768MB (not 0.25GB) because it's clamped at max_low_pfn: #ifdef CONFIG_ZONE_DMA max_zone_pfns[ZONE_DMA] =3D min(max_low_pfn, 1UL << (zone_dma_bits - PAGE_SHIFT)); #endif Which comes eventually from CONFIG_LOWMEM_SIZE, which defaults to 768MB. I think it's 768MB because the user:kernel split is 3G:1G, and then the kernel needs some of that 1G virtual space for vmalloc/ioremap/highmem, so it splits it 768M:256M. Then ZONE_NORMAL is empty because it is also limited to max_low_pfn: max_zone_pfns[ZONE_NORMAL] =3D max_low_pfn; The rest of RAM is highmem. So I think that's all behaving as expected, but I don't know 32-bit / highmem stuff that well so I could be wrong. cheers