From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mvJBx-00G0t5-CM for kexec@lists.infradead.org; Thu, 09 Dec 2021 13:10:36 +0000 Received: by mail-wr1-f70.google.com with SMTP id r2-20020adfe682000000b00198af042b0dso1377454wrm.23 for ; Thu, 09 Dec 2021 05:10:28 -0800 (PST) Message-ID: Date: Thu, 9 Dec 2021 14:10:25 +0100 MIME-Version: 1.0 Subject: Re: [PATCH RESEND v2 3/5] mm_zone: add function to check if managed dma zone exists References: <20211207030750.30824-1-bhe@redhat.com> <20211207030750.30824-4-bhe@redhat.com> <0a9bc228-21ba-abe3-d9c8-b9d52b936366@redhat.com> <20211209130210.GB3050@MiWiFi-R3L-srv> From: David Hildenbrand In-Reply-To: <20211209130210.GB3050@MiWiFi-R3L-srv> Content-Language: en-US List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Baoquan He Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, hch@lst.de, robin.murphy@arm.com, cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, vbabka@suse.cz, m.szyprowski@samsung.com, John.p.donnelly@oracle.com, kexec@lists.infradead.org On 09.12.21 14:02, Baoquan He wrote: > On 12/07/21 at 12:23pm, David Hildenbrand wrote: >> On 07.12.21 04:07, Baoquan He wrote: >>> In some places of the current kernel, it assumes that dma zone must have >>> managed pages if CONFIG_ZONE_DMA is enabled. 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. >>> >>> Signed-off-by: Baoquan He >>> --- >>> include/linux/mmzone.h | 21 +++++++++++++++++++++ >>> mm/page_alloc.c | 11 +++++++++++ >>> 2 files changed, 32 insertions(+) >>> >>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h >>> index 58e744b78c2c..82d23e13e0e5 100644 >>> --- a/include/linux/mmzone.h >>> +++ b/include/linux/mmzone.h >>> @@ -998,6 +998,18 @@ static inline bool zone_is_zone_device(struct zone *zone) >>> } >>> #endif >>> >>> +#ifdef CONFIG_ZONE_DMA >>> +static inline bool zone_is_dma(struct zone *zone) >>> +{ >>> + return zone_idx(zone) == ZONE_DMA; >>> +} >>> +#else >>> +static inline bool zone_is_dma(struct zone *zone) >>> +{ >>> + return false; >>> +} >>> +#endif >>> + >>> /* >>> * Returns true if a zone has pages managed by the buddy allocator. >>> * All the reclaim decisions have to use this function rather than >>> @@ -1046,6 +1058,7 @@ static inline int is_highmem_idx(enum zone_type idx) >>> #endif >>> } >>> >>> +bool has_managed_dma(void); >>> /** >>> * is_highmem - helper function to quickly check if a struct zone is a >>> * highmem zone or not. This is an attempt to keep references >>> @@ -1131,6 +1144,14 @@ extern struct zone *next_zone(struct zone *zone); >>> ; /* do nothing */ \ >>> else >>> >>> +#define for_each_managed_zone(zone) \ >>> + for (zone = (first_online_pgdat())->node_zones; \ >>> + zone; \ >>> + zone = next_zone(zone)) \ >>> + if (!managed_zone(zone)) \ >>> + ; /* do nothing */ \ >>> + else >>> + >>> static inline struct zone *zonelist_zone(struct zoneref *zoneref) >>> { >>> return zoneref->zone; >>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >>> index c5952749ad40..ac0ea42a4e5f 100644 >>> --- a/mm/page_alloc.c >>> +++ b/mm/page_alloc.c >>> @@ -9459,4 +9459,15 @@ bool take_page_off_buddy(struct page *page) >>> spin_unlock_irqrestore(&zone->lock, flags); >>> return ret; >>> } >>> + >>> +bool has_managed_dma(void) >>> +{ >>> + struct zone *zone; >>> + >>> + for_each_managed_zone(zone) { >>> + if (zone_is_dma(zone)) >>> + return true; >>> + } >>> + return false; >>> +} >> >> Wouldn't it be "easier/faster" to just iterate online nodes and directly >> obtain the ZONE_DMA, checking if there are managed pages? > > Thanks, Dave. > > Please check for_each_managed_zone(), it is iterating online nodes and > it's each managed zone. > > Is below what you are suggesting? The only difference is I introduced > for_each_managed_zone() which can be reused later if needed. Not sure if > I got your suggestion correctly. > > bool has_managed_dma(void) > { > struct pglist_data *pgdat; > struct zone *zone; > enum zone_type i, j; > > for_each_online_pgdat(pgdat) { > for (i = 0; i < MAX_NR_ZONES - 1; i++) { > struct zone *zone = &pgdat->node_zones[i]; > if (zone_is_dma(zone)) > return true; > } > } > return false; > > } Even simpler, no need to iterate over zones at all, only over nodes: #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 */ Without CONFIG_ZONE_DMA, simply provide a dummy in the header that returns false. -- Thanks, David / dhildenb _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec