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sp4UijFD2G35c3KJOQfI7Ra11b1GLXGjuK/z5i//X9keUQliHC88IoDDTbj/hbWyU7kX1+MMG013ugsYrvsNy4pXTkE+3ia58KRSllYgAiGhw15qSm3SrSlDu0mQGb4pmO/58Rsxa0J4aeFcKvAnvLcQomJRtw6HlWjTXjgERPbsf18OjwiTE33V4EjC/U2CQzw18JDYrIPXqBq1yOjSvx+TFxp2IVPHvR44OtcDANBFIY8AUivs6tl4G7N4SwzxtN10eLAqUprEGuY+an4TOFjoZMp7UxsWaIs1q0tGOGX1e9k1RRZWCNXheA5kENQSkHhqxqWeveJXgHT65rf7SD+nQxzRCVjcLuFUVgbBiuiYsQO0= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 3/14/23 02:49, Andrew Morton wrote: > On Mon, 13 Mar 2023 20:45:21 +0800 Yin Fengwei wrote: > >> This series is trying to bring the batched rmap removing to >> try_to_unmap_one(). It's expected that the batched rmap >> removing bring performance gain than remove rmap per page. >> >> This series reconstruct the try_to_unmap_one() from: >> loop: >> clear and update PTE >> unmap one page >> goto loop >> to: >> loop: >> clear and update PTE >> goto loop >> unmap the range of folio in one call >> It is one step to always map/unmap the entire folio in one call. >> Which can simplify the folio mapcount handling by avoid dealing >> with each page map/unmap. >> >> ... >> >> For performance gain demonstration, changed the MADV_PAGEOUT not >> to split the large folio for page cache and created a micro >> benchmark mainly as following: > > Please remind me why it's necessary to patch the kernel to actually > performance test this? And why it's proving so hard to demonstrate > benefits in real-world workloads? > > (Yes, this was touched on in earlier discussion, but I do think these > considerations should be spelled out in the [0/N] changelog). OK. What about add following in cover letter: " The performance gain of this series can be demonstrated with large folio reclaim. In current kernel, vmscan() path will be benefited by the changes. But there is no workload/benchmark can show the exact performance gain for vmscan() path as far as I am aware. Another way to demonstrate the performance benefit is using MADV_PAGEOUT which can trigger page reclaim also. The problem is that MADV_PAGEOUT always split the large folio because it's not aware of large folio for page cache currently. To show the performance benefit, MADV_PAGEOUT is updated not to split the large folio. For long term with wider adoption of large folio in kernel (like large folio for anonymous page), MADV_PAGEOUT needs be updated to handle large folio as whole to avoid splitting it always. " Regards Yin, Fengwei > > Thanks.