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(p200300cbc70574006b3aa74abd53a018.dip0.t-ipconnect.de. [2003:cb:c705:7400:6b3a:a74a:bd53:a018]) by smtp.gmail.com with ESMTPSA id g4-20020a5d5404000000b0021d7b999949sm10521072wrv.111.2022.07.18.03.48.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 18 Jul 2022 03:48:09 -0700 (PDT) Message-ID: <488f510f-00ad-4ef0-1eb9-ac73c7bb527c@redhat.com> Date: Mon, 18 Jul 2022 12:48:08 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Content-Language: en-US To: Vaibhav Jain , linux-kernel@vger.kernel.org Cc: "Aneesh Kumar K . V" , Andrew Morton , Dan Williams , Miaohe Lin , Muchun Song References: <20220601163243.3806231-1-vaibhav@linux.ibm.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH] resource: re-factor page_is_ram() In-Reply-To: <20220601163243.3806231-1-vaibhav@linux.ibm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01.06.22 18:32, Vaibhav Jain wrote: > Presently page_is_ram() relies on walk_system_ram_range() that performs a walk > on kernel iomem resources hierarchy with a dummy callback __is_ram(). Before > calling find_next_iomem_res(), walk_system_ram_range() does some book-keeping > which can be avoided for page_is_ram() use-case. > > Hence this patch proposes to update page_is_ram() to directly call > find_next_iomem_res() with minimal book-keeping needed. > > To avoid allocating a 'struct resource' the patch also updates > find_next_iomem_res() to not return -EINVAL in case 'res == NULL'. Instead > out 'struct resource *res' is only populated when its not NULL. > > Signed-off-by: Vaibhav Jain > --- > kernel/resource.c | 19 ++++++++----------- > 1 file changed, 8 insertions(+), 11 deletions(-) > > diff --git a/kernel/resource.c b/kernel/resource.c > index 34eaee179689..ecf6b9a50adc 100644 > --- a/kernel/resource.c > +++ b/kernel/resource.c > @@ -311,7 +311,7 @@ EXPORT_SYMBOL(release_resource); > * > * If a resource is found, returns 0 and @*res is overwritten with the part > * of the resource that's within [@start..@end]; if none is found, returns > - * -ENODEV. Returns -EINVAL for invalid parameters. > + * -ENODEV. > * There is still another -EINVAL in that function ... > * @start: start address of the resource searched for > * @end: end address of same resource > @@ -328,9 +328,6 @@ static int find_next_iomem_res(resource_size_t start, resource_size_t end, > { > struct resource *p; > > - if (!res) > - return -EINVAL; > - > if (start >= end) > return -EINVAL; As all callers guarantee that, we might just remove it. > > @@ -356,7 +353,7 @@ static int find_next_iomem_res(resource_size_t start, resource_size_t end, > break; > } > > - if (p) { > + if (p && res) { > /* copy data */ > *res = (struct resource) { > .start = max(start, p->start), > @@ -474,18 +471,18 @@ int walk_system_ram_range(unsigned long start_pfn, unsigned long nr_pages, > return ret; > } > > -static int __is_ram(unsigned long pfn, unsigned long nr_pages, void *arg) > -{ > - return 1; > -} > - > /* > * This generic page_is_ram() returns true if specified address is > * registered as System RAM in iomem_resource list. > */ > int __weak page_is_ram(unsigned long pfn) > { > - return walk_system_ram_range(pfn, 1, NULL, __is_ram) == 1; > + const resource_size_t pfn_res = PFN_PHYS(pfn); > + > + return find_next_iomem_res(pfn_res, > + pfn_res + 1, > + IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY, > + IORES_DESC_NONE, NULL) == 0; > } > EXPORT_SYMBOL_GPL(page_is_ram); > What about a) A cleanup patch upfront that removes both -EINVAL cases from find_next_iomem_res() followed by b) The actual change to page_is_ram() ? -- Thanks, David / dhildenb