On Thu, Jun 15, 2023 at 9:41 PM 贺中坤 <hezhongkun.hzk@xxxxxxxxxxxxx> wrote: > > > Thanks Fabian for tagging me. > > > > I am not familiar with #1, so I will speak to #2. Zhongkun, There are > > a few parts that I do not understand -- hopefully you can help me out > > here: > > > > (1) If I understand correctly in this patch we set the active memcg > > trying to charge any pages allocated in a zspage to the current memcg, > > yet that zspage will contain multiple compressed object slots, not > > just the one used by this memcg. Aren't we overcharging the memcg? > > Basically the first memcg that happens to allocate the zspage will pay > > for all the objects in this zspage, even after it stops using the > > zspage completely? > > It will not overcharge. As you said below, we are not using > __GFP_ACCOUNT and charging the compressed slots to the memcgs. > > > > > (2) Patch 3 seems to be charging the compressed slots to the memcgs, > > yet this patch is trying to charge the entire zspage. Aren't we double > > charging the zspage? I am guessing this isn't happening because (as > > Michal pointed out) we are not using __GFP_ACCOUNT here anyway, so > > this patch may be NOP, and the actual charging is coming from patch 3 > > only. > > YES， the actual charging is coming from patch 3. This patch just > delivers the BIO page's memcg to the current task which is not the > consumer. > > > > > (3) Zswap recently implemented per-memcg charging of compressed > > objects in a much simpler way. If your main interest is #2 (which is > > what I understand from the commit log), it seems like zswap might be > > providing this already? Why can't you use zswap? Is it the fact that > > zswap requires a backing swapfile? > > Thanks for your reply and review. Yes, the zswap requires a backing > swapfile. The I/O path is very complex, sometimes it will throttle the > whole system if some resources are short , so we hope to use zram. Is the only problem with zswap for you the requirement of a backing swapfile? If yes, I am in the early stages of developing a solution to make zswap work without a backing swapfile. This was discussed in LSF/MM [1]. Would this make zswap usable in for your use case? [1]https://lore.kernel.org/linux-mm/CAJD7tkYb_sGN8mfGVjr2JxdB8Pz8Td=yj9_sBCMrmsKQo56vTg@xxxxxxxxxxxxxx/ > > > > > Thanks! > >
