From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mvJ4P-00G00k-7R for kexec@lists.infradead.org; Thu, 09 Dec 2021 13:02:47 +0000 Date: Thu, 9 Dec 2021 21:02:10 +0800 From: Baoquan He Subject: Re: [PATCH RESEND v2 3/5] mm_zone: add function to check if managed dma zone exists Message-ID: <20211209130210.GB3050@MiWiFi-R3L-srv> References: <20211207030750.30824-1-bhe@redhat.com> <20211207030750.30824-4-bhe@redhat.com> <0a9bc228-21ba-abe3-d9c8-b9d52b936366@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <0a9bc228-21ba-abe3-d9c8-b9d52b936366@redhat.com> 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: David Hildenbrand 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 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; } _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec