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[2003:cb:c705:4200:6374:a71a:a88:a4b]) by smtp.gmail.com with ESMTPSA id k40-20020a05600c1ca800b0038c6c8b7fa8sm9619012wms.25.2022.03.25.13.19.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 25 Mar 2022 13:19:52 -0700 (PDT) Message-ID: <7f3a973f-1f0c-4e50-2528-b0e9dc3e4cac@redhat.com> Date: Fri, 25 Mar 2022 21:19:51 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.2 Subject: Re: [PATCH v3] mm/vmstat: add events for ksm cow Content-Language: en-US To: Andrew Morton , cgel.zte@gmail.com Cc: yang.yang29@zte.com.cn, ran.xiaokai@zte.com.cn, yang.shi@linux.alibaba.com, dave.hansen@linux.intel.com, minchan@kernel.org, saravanand@fb.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, xu xin References: <20220324104332.2350482-1-yang.yang29@zte.com.cn> <20220325130957.171a68dee88118082ab841c5@linux-foundation.org> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20220325130957.171a68dee88118082ab841c5@linux-foundation.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 25.03.22 21:09, Andrew Morton wrote: > On Thu, 24 Mar 2022 10:43:33 +0000 cgel.zte@gmail.com wrote: > >> From: Yang Yang >> >> Users may use ksm by calling madvise(, , MADV_MERGEABLE) when they want >> to save memory, it's a tradeoff by suffering delay on ksm cow. Users can >> get to know how much memory ksm saved by reading >> /sys/kernel/mm/ksm/pages_sharing, but they don't know what's the costs >> of ksm cow, and this is important of some delay sensitive tasks. >> >> So add ksm cow events to help users evaluate whether or how to use ksm. > > It's unclear (to me) how anyone will actually use this, how they will > interpret the output. > > Some tutorial words added to Documentation/vm/ksm.rst would be helpful. > While in there, please check for any other /proc/vmstat fields which > we forgot to document. > >> --- a/include/linux/vm_event_item.h >> +++ b/include/linux/vm_event_item.h >> @@ -131,6 +131,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT, >> SWAP_RA_HIT, >> #ifdef CONFIG_KSM >> KSM_SWPIN_COPY, >> + COW_KSM, > > I agree that this name looks unpleasingly backwards. Do we have an > expectation that we actually will be adding more COW_* fields? As raised previously (also when proposing this), I'd like to have COW_ANON, COW_ZERO, COW_OTHER. Ideally, we'd have added all via a single patch for them. They would at least be of value to me. -- Thanks, David / dhildenb