Hi Bijan, Subjects of patches usually be converted into lowercase when be merged into mm tree. I'd suggest using lowercase even in patches stage, if those aim to be merged into mm tree. On Tue, 5 Aug 2025 11:20:17 -0500 Bijan Tabatabai <bijan311@xxxxxxxxx> wrote: > From: Bijan Tabatabai <bijantabatab@xxxxxxxxxx> > > This patchset adds two DAMON commands, commit_schemes_dests and > wait_for_schemes_apply, that I have found useful for using a migrate_hot > scheme with migration dests. Thank you for this patchset! I believe we shouldn't be afraid at adding features, but should also be carefult at making good solutions for real problems. So, my main response to this patchset is, hopefully unsurprisingly, I'd like to better understand the requirements and the problem you are encountering. > > The commit_schemes_dests command, similar to the existing > commit_schemes_quota_goals, is used to commit only the dests fields of > schemes. This has a couple of benefits: > 1) It is more efficient than recommitting all the DAMON data. > 2) Doing a full commit resets the aggregation and ops_update intervals. If > a user sends the full commit command frequently (relatively to those > intervals) the aggregation and ops_update events will be prevented from > triggering. Having a separate commit command side steps this problem. I agree the commit command of DAMON sysfs interface is inefficient, and could make the infinite intervals delay problem. But, I didn't expect there could be use cases that use commit feature frequently enough to make the inefficiency and the intervals delay be real problems. Could you please let me know more details about your use case and how severe problem DAMON is causing? Depending on the real problem, I'm wondering if optimizing commit command can be a solution. For example, skipping the update of next_aggregation_sis and next_ops_update_sis when the intervals are not changed might be able to solve the intervals delay problem. > > The wait_for_schemes_apply command causes the calling thread to wait until > all schemes have been applied. It does this by calling damos_walk() with a > NULL walk_fn. This can be useful, for example, if a user wants to know when > new scheme parameters they've committed have been applied. Another use case > could be if a user wants to record the system state every time a scheme is > applied for debuging purposes. > > The functionality of wait_for_schemes_apply can be achieved with the > existing update_schemes_tried_bytes and update_schemes_tried_regions > commands. However, having a separate command avoids extra work and makes > user intent clearer when used in scripts. I agree extra works are always better to be avoided. But is the overhead large enough to be a real problem for your use case? I also agree it could make the user script cleaner, but adding a kernel feature only for user scripts readabilities sounds like too much, since the user script could have its own abstract layers for its readability. Also, even if the new command is implemented, since the DAMOS schemes continue running, the system status will keep changing. If you cannot do the recording of the system state in a restricted time, the recorded information might not be that reliable. So I'm not sure if you really need this strict waiting in this way. Could you please share more details about what you want to do with the new command, and how much problem you are seeing? I'm particularly curious what system state you want to record, and why you need to wait the exact time interval. Depending on the real use case and the problem, I think we might be able to reuse the DAMOS scheme stats, or implement more strict and reliable time control features, say, making kdamond or schemes pause and resume as users ask? Thanks, SJ [...]
