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[2003:cb:c702:b500:3ed7:a1c7:447e:2279]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4264a21d2adsm53334365e9.29.2024.07.05.02.16.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 05 Jul 2024 02:16:22 -0700 (PDT) Message-ID: Date: Fri, 5 Jul 2024 11:16:21 +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> <32f04739-0cd0-4a9e-9419-c5a13c333c28@redhat.com> <8d3804ad-14c8-4041-8f52-58fd9dd8d4b4@arm.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 05.07.24 11:13, Ryan Roberts wrote: > On 05/07/2024 09:59, David Hildenbrand wrote: >> 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. > > That approach is exactly what I proposed to start playing with yesterday [1] for > regular pagecache folio allocations too :) In German, there is this saying "zwei Dumme ein Gedanke". The official English alternative is "great minds think alike". ... well, the direct German->English translation definitely has a "German touch" to it: "two stupid ones one thought" -- Cheers, David / dhildenb