On Thu, Sep 5, 2024 at 7:36 AM Yosry Ahmed <yosryahmed@xxxxxxxxxx> wrote: > > [..] > > > > > > On the other hand, if you read the code of zRAM, you will find zRAM has > > > exactly the same mechanism as zeromap but zRAM can even do more > > > by same_pages filled. since zRAM does the job in swapfile layer, there > > > is no this kind of consistency issue like zeromap. > > > > > > So I feel for zRAM case, we don't need zeromap at all as there are duplicated > > > efforts while I really appreciate your job which can benefit all swapfiles. > > > i mean, zRAM has the ability to check "zero"(and also non-zero but same > > > content). after zeromap checks zeromap, zRAM will check again: > > > > > > > Yes, so there is a reason for having the zeromap patches, which I have outlined > > in the coverletter. > > > > https://lore.kernel.org/all/20240627105730.3110705-1-usamaarif642@xxxxxxxxx/ > > > > There are usecases where zswap/zram might not be used in production. > > We can reduce I/O and flash wear in those cases by a large amount. > > > > Also running in Meta production, we found that the number of non-zero filled > > complete pages were less than 1%, so essentially its only the zero-filled pages > > that matter. > > > > I believe after zeromap, it might be a good idea to remove the page_same_filled > > check from zram code? Its not really a problem if its kept as well as I dont > > believe any zero-filled pages should reach zram_write_page? > > I brought this up before and Sergey pointed out that zram is sometimes > used as a block device without swap, and that use case would benefit > from having this handling in zram. That being said, I have no idea how > many people care about this specific scenario. Hi Usama/Yosry, We successfully gathered page_same_filled data for zram on Android. Interestingly, our findings differ from yours on zswap. Hailong discovered that around 85-86% of the page_same_filled data consists of zeros, while about 15% are non-zero. We suspect that on Android or similar systems, some graphics or media data might be duplicated at times, such as a red block displayed on the screen. Does this suggest that page_same_filled could still provide some benefits in zram cases? Thanks Barry
