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Mon, 13 Dec 2021 14:22:19 +0000 Message-ID: Date: Mon, 13 Dec 2021 08:22:13 -0600 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0) Gecko/20100101 Thunderbird/91.4.0 Subject: Re: [PATCH v3 3/5] mm_zone: add function to check if managed dma zone exists Content-Language: en-US To: Baoquan He , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, akpm@linux-foundation.org, hch@lst.de, cl@linux.com, John.p.donnelly@oracle.com, kexec@lists.infradead.org, stable@vger.kernel.org References: <20211213122712.23805-1-bhe@redhat.com> <20211213122712.23805-4-bhe@redhat.com> From: john.p.donnelly@oracle.com In-Reply-To: <20211213122712.23805-4-bhe@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: YT3PR01CA0143.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:b01:83::28) To CO1PR10MB4722.namprd10.prod.outlook.com (2603:10b6:303:9e::12) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 137eeb7f-b26a-4964-65ff-08d9be43f867 X-MS-TrafficTypeDiagnostic: MWHPR10MB1517:EE_ X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:5797; 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While this is not always true. > E.g in kdump kernel of x86_64, only low 1M is presented and locked down > at very early stage of boot, so that there's no managed pages at all in > DMA zone. This exception will always cause page allocation failure if page > is requested from DMA zone. > > Here add function has_managed_dma() and the relevant helper functions to > check if there's DMA zone with managed pages. It will be used in later > patches. > > Fixes: 6f599d84231f ("x86/kdump: Always reserve the low 1M when the crashkernel option is specified") > Cc: stable@vger.kernel.org > Signed-off-by: Baoquan He > Acked-by: John Donnelly Tested-by: John Donnelly > --- > v2->v3: > Rewrite has_managed_dma() in a simpler and more efficient way which is > sugggested by DavidH. > > include/linux/mmzone.h | 9 +++++++++ > mm/page_alloc.c | 15 +++++++++++++++ > 2 files changed, 24 insertions(+) > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index 58e744b78c2c..6e1b726e9adf 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -1046,6 +1046,15 @@ static inline int is_highmem_idx(enum zone_type idx) > #endif > } > > +#ifdef CONFIG_ZONE_DMA > +bool has_managed_dma(void); > +#else > +static inline bool has_managed_dma(void) > +{ > + return false; > +} > +#endif > + > /** > * is_highmem - helper function to quickly check if a struct zone is a > * highmem zone or not. This is an attempt to keep references > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index c5952749ad40..7c7a0b5de2ff 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -9460,3 +9460,18 @@ bool take_page_off_buddy(struct page *page) > return ret; > } > #endif > + > +#ifdef CONFIG_ZONE_DMA > +bool has_managed_dma(void) > +{ > + struct pglist_data *pgdat; > + > + for_each_online_pgdat(pgdat) { > + struct zone *zone = &pgdat->node_zones[ZONE_DMA]; > + > + if (managed_zone(zone)) > + return true; > + } > + return false; > +} > +#endif /* CONFIG_ZONE_DMA */