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From: "Yajun Deng" Message-ID: Subject: Re: [PATCH] mm/mm_init.c: remove spinlock in early_pfn_to_nid() To: "Mike Rapoport" Cc: "Greg KH" , rafael@kernel.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org In-Reply-To: <20230614115339.GX52412@kernel.org> References: <20230614115339.GX52412@kernel.org> <2023061431-litigate-upchuck-7ed1@gregkh> <20230614110324.3839354-1-yajun.deng@linux.dev> X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org June 14, 2023 7:53 PM, "Mike Rapoport" wrote:=0A=0A> Hi= ,=0A> =0A> On Wed, Jun 14, 2023 at 11:28:32AM +0000, Yajun Deng wrote:=0A= > =0A>> June 14, 2023 7:09 PM, "Greg KH" wro= te:=0A>> =0A>> On Wed, Jun 14, 2023 at 07:03:24PM +0800, Yajun Deng wrote= :=0A>> =0A>> When the system boots, only one cpu is enabled before smp_in= it().=0A>> So the spinlock is not needed in most cases, remove it.=0A>> = =0A>> Add spinlock in get_nid_for_pfn() because it is after smp_init().= =0A>> =0A>> So this is two different things at once in the same patch?=0A= >> =0A>> Or are they the same problem and both need to go in to solve it?= =0A>> =0A>> And if a spinlock is not needed at early boot, is it really c= ausing any=0A>> problems?=0A>> =0A>> They are the same problem.=0A>> I ad= ded pr_info in early_pfn_to_nid(), found get_nid_for_pfn() is the only=0A= >> case need to add spinlock.=0A>> This patch tested on my x86 system.=0A= > =0A> Are you sure it'll work on !x86?=0A>=0A=0AI'm probably sure of tha= t, although I don't have a !x86 machine.=0A=0Aearly_pfn_to_nid() is calle= d in smp_init() and kasan_init() on =0Adifferent architectures. If it wor= ks well on x86, it'll work on=0A!x86.=0A=0A =0A>> Signed-off-by: Yajun De= ng =0A>> ---=0A>> drivers/base/node.c | 11 ++++++++= +--=0A>> mm/mm_init.c | 18 +++---------------=0A>> 2 files changed, 12 in= sertions(+), 17 deletions(-)=0A>> =0A>> diff --git a/drivers/base/node.c = b/drivers/base/node.c=0A>> index 9de524e56307..844102570ff2 100644=0A>> -= -- a/drivers/base/node.c=0A>> +++ b/drivers/base/node.c=0A>> @@ -748,8 +7= 48,15 @@ int unregister_cpu_under_node(unsigned int cpu, unsigned int nid= )=0A>> static int __ref get_nid_for_pfn(unsigned long pfn)=0A>> {=0A>> #i= fdef CONFIG_DEFERRED_STRUCT_PAGE_INIT=0A>> - if (system_state < SYSTEM_RU= NNING)=0A>> - return early_pfn_to_nid(pfn);=0A>> + static DEFINE_SPINLOCK= (early_pfn_lock);=0A>> + int nid;=0A>> +=0A>> + if (system_state < SYSTEM= _RUNNING) {=0A>> + spin_lock(&early_pfn_lock);=0A>> + nid =3D early_pfn_t= o_nid(pfn);=0A>> + spin_unlock(&early_pfn_lock);=0A>> =0A>> Adding an ext= ernal lock for when you call a function is VERY dangerous=0A>> as you did= not document this anywhere, and there's no way to enforce it=0A>> proper= ly at all.=0A>> =0A>> I should add a comment before early_pfn_to_nid().= =0A>> =0A>> Does your change actually result in any boot time changes? Ho= w was this=0A>> tested?=0A>> =0A>> Just a bit.=0A> =0A> Just a bit tested= ? Or just a bit of boot time changes?=0A> For the latter, do you have num= bers?=0A> =0A=0AFor the latter, the most beneficial function is memmap_in= it_reserved_pages(),=0Athe boot time changes depending on whether DEFERRE= D_STRUCT_PAGE_INIT=0Ais defined or not. =0A=0A-->memmap_init_reserved_pag= es()=0A -->for_each_reserved_mem_range()=0A reserve_bootmem_region= ()=0A -->for()=0A init_reserved_page()=0A --> early_= pfn_to_nid()=0A=0A=0AIf define CONFIG_DEFERRED_STRUCT_PAGE_INIT:=0A=0Abef= ore:=0Amemmap_init_reserved_pages() 1.87 seconds=0Aafter:=0Amemmap_init= _reserved_pages() 1.27 seconds=0A=0A32% time reduction.=0A=0A=0AIf not = define CONFIG_DEFERRED_STRUCT_PAGE_INIT:=0A=0Aearly_pfn_to_nid() is calle= d by few, =0Aboot time didn't change.=0A=0A=0ABy the way, this machine ha= s 190GB RAM.=0A=0A> --=0A> Sincerely yours,=0A> Mike.