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[2003:cb:c702:b500:3ed7:a1c7:447e:2279]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-42651531f1fsm17678905e9.0.2024.07.05.01.59.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 05 Jul 2024 01:59:03 -0700 (PDT) Message-ID: <32f04739-0cd0-4a9e-9419-c5a13c333c28@redhat.com> Date: Fri, 5 Jul 2024 10:59:02 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 0/6] add mTHP support for anonymous shmem To: Ryan Roberts , Baolin Wang , Matthew Wilcox Cc: akpm@linux-foundation.org, hughd@google.com, wangkefeng.wang@huawei.com, ying.huang@intel.com, 21cnbao@gmail.com, shy828301@gmail.com, ziy@nvidia.com, ioworker0@gmail.com, da.gomez@samsung.com, p.raghav@samsung.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <27beaa0e-697e-4e30-9ac6-5de22228aec1@redhat.com> <6d4c0191-18a9-4c8f-8814-d4775557383e@redhat.com> Content-Language: en-US From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 05.07.24 10:45, Ryan Roberts wrote: > On 05/07/2024 06:47, Baolin Wang wrote: >> >> >> On 2024/7/5 03:49, Matthew Wilcox wrote: >>> On Thu, Jul 04, 2024 at 09:19:10PM +0200, David Hildenbrand wrote: >>>> On 04.07.24 21:03, David Hildenbrand wrote: >>>>>> shmem has two uses: >>>>>> >>>>>>     - MAP_ANONYMOUS | MAP_SHARED (this patch set) >>>>>>     - tmpfs >>>>>> >>>>>> For the second use case we don't want controls *at all*, we want the >>>>>> same heiristics used for all other filesystems to apply to tmpfs. >>>>> >>>>> As discussed in the MM meeting, Hugh had a different opinion on that. >>>> >>>> FWIW, I just recalled that I wrote a quick summary: >>>> >>>> https://lkml.kernel.org/r/f1783ff0-65bd-4b2b-8952-52b6822a0835@redhat.com >>>> >>>> I believe the meetings are recorded as well, but never looked at recordings. >>> >>> That's not what I understood Hugh to mean.  To me, it seemed that Hugh >>> was expressing an opinion on using shmem as shmem, not as using it as >>> tmpfs. >>> >>> If I misunderstood Hugh, well, I still disagree.  We should not have >>> separate controls for this.  tmpfs is just not that special. > > I wasn't at the meeting that's being referred to, but I thought we previously > agreed that tmpfs *is* special because in some configurations its not backed by > swap so is locked in ram? There are multiple things to that, like: * Machines only having limited/no swap configured * tmpfs can be configured to never go to swap * memfd/tmpfs files getting used purely for mmap(): there is no real difference to MAP_ANON|MAP_SHARE besides the processes we share that memory with. Especially when it comes to memory waste concerns and access behavior in some cases, tmpfs behaved much more like anonymous memory. But there are for sure other use cases where tmpfs is not that special. My opinion is that we need to let people configure orders (if you feel like it, configure all), but *select* the order to allocate based on readahead information -- in contrast to anonymous memory where we start at the highest order and don't have readahead information available. Maybe we need different "order allcoation" logic for read/write vs. fault, not sure. But I don't maintain that code, so I can only give stupid suggestions and repeat what I understood from the meeting with Hugh and Kirill :) -- Cheers, David / dhildenb