On Thu, 26 Nov 2020 12:51:57 +0100 SeongJae Park <sjpark@xxxxxxxxxx> wrote: > Hi Shakeel, > > > Thanks for the review! :D > > On Wed, 25 Nov 2020 07:29:10 -0800 Shakeel Butt <shakeelb@xxxxxxxxxx> wrote: > > > On Tue, Oct 20, 2020 at 2:01 AM SeongJae Park <sjpark@xxxxxxxxxx> wrote: > > > > > > From: SeongJae Park <sjpark@xxxxxxxxx> > > > > > > DAMON is a data access monitoring framework for the Linux kernel. The > > > core mechanisms of DAMON make it > > > > > > - accurate (the monitoring output is useful enough for DRAM level > > > performance-centric memory management; It might be inappropriate for > > > CPU Cache levels, though), > > > - light-weight (the monitoring overhead is normally low enough to be > > > applied online), and > > > - scalable (the upper-bound of the overhead is in constant range > > > regardless of the size of target workloads). > > > > > > Using this framework, hence, we can easily write efficient kernel space > > > data access monitoring applications. For example, the kernel's memory > > > management mechanisms can make advanced decisions using this. > > > Experimental data access aware optimization works that incurring high > > > access monitoring overhead could implemented again on top of this. > > > > > > Due to its simple and flexible interface, providing user space interface > > > would be also easy. Then, user space users who have some special > > > workloads can write personalized applications for better understanding > > > and optimizations of their workloads and systems. > > > > > > That said, this commit is implementing only basic data structures and > > > simple manipulation functions of the structures. The core mechanisms of > > > DAMON will be implemented by following commits. > > > > > > Signed-off-by: SeongJae Park <sjpark@xxxxxxxxx> > > > Reviewed-by: Leonard Foerster <foersleo@xxxxxxxxx> > > > Reviewed-by: Varad Gautam <vrd@xxxxxxxxx> > > [...] > > I would suggest to separate > > the core (damon context) from the target related structs (target, > > region, addr range). > > To be honest, I unsure if I'm fully understanding what specific change you want > to make. So if I'm misunderstanding your point below, please let me know. > > Seems like you are concerning for future support of special kind use cases that > don't need targets/regions/addresses, such as page granularity monitoring that > having interest in only if the pages accessed or not, rather than access > frequency. In the context, your suggestion makes sense as the region > abstraction is only burden in the case, as I also mentioned in the cover > letter. This could be done via idle pages tracking, but DAMON will be able to > do this faster by reducing the number of user-kernel context switches. > > I once considered adding some change in the core part for efficient support of > such use cases, but resulted in believing that the best way for that is > implementing another primitive for the case and use it in a controlled way. > > In a high level, it should disable the 'adaptive regions adjustment' feature > and define it's own targets structs other than the damon_target. Then, your > implementation of the primitive callbacks should use your own targets. > > In more detail, the 'adaptive regions adjustment' can be disabled by setting > the min_nr_regions and max_nr_regions of the damon_ctx with same value, say, 0. > Your own targets structs could be stored in 'damon_callback->private'. Or, we > could add another 'private' field in damon_ctx for that. > > I think this will work, but I also admit that this could look like a hairy > hack to someone. Fundamentally, this is because the region based > overhead/accuracy handling is strongly coupled in the design. So, I think what > you are really suggesting is making DAMON more general by default and > supporting the region based overhead/accuracy handling additionally. > > If I'm understanding correctly, how about below like change? Obviously this > should be cleaned up a lot, but I just want to quickly share my idea and > discuss. Also note that it's based on the damon/next tree[1]. > > [1] https://github.com/sjp38/linux/tree/damon/next > > +enum damon_type { > + ARBITRARY_TARGETS, > + ADAPTIVE_REGIONS, > +}; > + > +struct damon_adaptive_regions_ctx { > + unsigned long min_nr_regions; > + unsigned long max_nr_regions; > + struct list_head targets; > + struct list_head schemes; > +}; > + > /** > * struct damon_ctx - Represents a context for each monitoring. This is the > * main interface that allows users to set the attributes and get the results > @@ -243,8 +255,6 @@ struct damon_ctx { > unsigned long sample_interval; > unsigned long aggr_interval; > unsigned long regions_update_interval; > - unsigned long min_nr_regions; > - unsigned long max_nr_regions; > > struct timespec64 last_aggregation; > struct timespec64 last_regions_update; > @@ -253,11 +263,14 @@ struct damon_ctx { > bool kdamond_stop; > struct mutex kdamond_lock; > > - struct list_head targets_list; /* 'damon_target' objects */ > - struct list_head schemes_list; /* 'damos' objects */ > - > struct damon_primitive primitive; > struct damon_callback callback; > + > + enum damon_type type; > + union { > + struct damon_adaptive_regions_ctx arctx; > + void *targets; > + }; > }; > > The patchset will first introduce DAMON as only ARBITRARY_TARGETS (or, would > TINY be a better name?) type supporting form. After that, following patch will > add ADAPTIVE_REGIONS type support. Do you think I'm correctly understanding > your point and above suggestion makes sense? In a private message, Shakeel confirmed I'm correnctly understanding his intention and asked next version. I will post next version soon. Thanks, SeongJae Park
