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Thu, 9 Apr 2020 02:59:16 +0000 (UTC) Received: from [10.72.8.19] (ovpn-8-19.pek2.redhat.com [10.72.8.19]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0879FC0DA3; Thu, 9 Apr 2020 02:59:06 +0000 (UTC) Subject: Re: [PATCH v1 1/2] powerpc/pseries/hotplug-memory: stop checking is_mem_section_removable() To: Baoquan He , David Hildenbrand References: <20200407135416.24093-1-david@redhat.com> <20200407135416.24093-2-david@redhat.com> <20200408024630.GQ2402@MiWiFi-R3L-srv> From: piliu X-Enigmail-Draft-Status: N1110 Message-ID: <16187f69-0e5b-c9c2-a31b-8658425758aa@redhat.com> Date: Thu, 9 Apr 2020 10:59:02 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <20200408024630.GQ2402@MiWiFi-R3L-srv> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Michal Hocko , linux-kernel@vger.kernel.org, Wei Yang , linux-mm@kvack.org, Paul Mackerras , Nathan Fontenot , Andrew Morton , linuxppc-dev@lists.ozlabs.org, Oscar Salvador Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 04/08/2020 10:46 AM, Baoquan He wrote: > Add Pingfan to CC since he usually handles ppc related bugs for RHEL. > > On 04/07/20 at 03:54pm, David Hildenbrand wrote: >> In commit 53cdc1cb29e8 ("drivers/base/memory.c: indicate all memory >> blocks as removable"), the user space interface to compute whether a memory >> block can be offlined (exposed via >> /sys/devices/system/memory/memoryX/removable) has effectively been >> deprecated. We want to remove the leftovers of the kernel implementation. > > Pingfan, can you have a look at this change on PPC? Please feel free to > give comments if any concern, or offer ack if it's OK to you. > >> >> When offlining a memory block (mm/memory_hotplug.c:__offline_pages()), >> we'll start by: >> 1. Testing if it contains any holes, and reject if so >> 2. Testing if pages belong to different zones, and reject if so >> 3. Isolating the page range, checking if it contains any unmovable pages >> >> Using is_mem_section_removable() before trying to offline is not only racy, >> it can easily result in false positives/negatives. Let's stop manually >> checking is_mem_section_removable(), and let device_offline() handle it >> completely instead. We can remove the racy is_mem_section_removable() >> implementation next. >> >> We now take more locks (e.g., memory hotplug lock when offlining and the >> zone lock when isolating), but maybe we should optimize that >> implementation instead if this ever becomes a real problem (after all, >> memory unplug is already an expensive operation). We started using >> is_mem_section_removable() in commit 51925fb3c5c9 ("powerpc/pseries: >> Implement memory hotplug remove in the kernel"), with the initial >> hotremove support of lmbs. >> >> Cc: Nathan Fontenot >> Cc: Michael Ellerman >> Cc: Benjamin Herrenschmidt >> Cc: Paul Mackerras >> Cc: Michal Hocko >> Cc: Andrew Morton >> Cc: Oscar Salvador >> Cc: Baoquan He >> Cc: Wei Yang >> Signed-off-by: David Hildenbrand >> --- >> .../platforms/pseries/hotplug-memory.c | 26 +++---------------- >> 1 file changed, 3 insertions(+), 23 deletions(-) >> >> diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c >> index b2cde1732301..5ace2f9a277e 100644 >> --- a/arch/powerpc/platforms/pseries/hotplug-memory.c >> +++ b/arch/powerpc/platforms/pseries/hotplug-memory.c >> @@ -337,39 +337,19 @@ static int pseries_remove_mem_node(struct device_node *np) >> >> static bool lmb_is_removable(struct drmem_lmb *lmb) >> { >> - int i, scns_per_block; >> - bool rc = true; >> - unsigned long pfn, block_sz; >> - u64 phys_addr; >> - >> if (!(lmb->flags & DRCONF_MEM_ASSIGNED)) >> return false; >> >> - block_sz = memory_block_size_bytes(); >> - scns_per_block = block_sz / MIN_MEMORY_BLOCK_SIZE; >> - phys_addr = lmb->base_addr; >> - >> #ifdef CONFIG_FA_DUMP >> /* >> * Don't hot-remove memory that falls in fadump boot memory area >> * and memory that is reserved for capturing old kernel memory. >> */ >> - if (is_fadump_memory_area(phys_addr, block_sz)) >> + if (is_fadump_memory_area(lmb->base_addr, memory_block_size_bytes())) >> return false; >> #endif >> - >> - for (i = 0; i < scns_per_block; i++) { >> - pfn = PFN_DOWN(phys_addr); >> - if (!pfn_in_present_section(pfn)) { >> - phys_addr += MIN_MEMORY_BLOCK_SIZE; >> - continue; >> - } >> - >> - rc = rc && is_mem_section_removable(pfn, PAGES_PER_SECTION); >> - phys_addr += MIN_MEMORY_BLOCK_SIZE; >> - } >> - >> - return rc; >> + /* device_offline() will determine if we can actually remove this lmb */ >> + return true; So I think here swaps the check and do sequence. At least it breaks dlpar_memory_remove_by_count(). It is doable to remove is_mem_section_removable(), but here should be more effort to re-arrange the code. Thanks, Pingfan >> } >> >> static int dlpar_add_lmb(struct drmem_lmb *); >> -- >> 2.25.1 >>