On 2020-06-15T18:19:16+02:00 SeongJae Park <sjpark@xxxxxxxxxx> wrote: > From: SeongJae Park <sjpark@xxxxxxxxx> > > This commit implements DAMON's target address space independent high > level logics for basic access check and region based sampling. The > target address space specific logics for the monitoring target address > regions construction and the access check are required, though. The > following commits will provide reference implementations of those for > the general virtual address spaces and the physical address space. > Users can implement and use their own versions for their specific use > cases, though. > > Basic Access Check > ------------------ > > DAMON basically reports what pages are how frequently accessed. The > frequency is not an absolute number of accesses, but a ratio. > > For this, DAMON first calls target monitoring construction callback > (``init_target_regions``), and then the access check callbacks, which is > assumed to check the access to each page and aggregates the number of > observed accesses of each page, for every ``sampling interval``. > Finally, DAMON resets the aggregated count per ``aggregation interval``. > > This is thus similar to the common periodic access checks based > monitoring mechanisms but provides the access frequency. The overhead > will increase as the size of the target process grows. > > Region Based Sampling > --------------------- > > To avoid the unbounded increase of the overhead, DAMON groups a number > of adjacent pages that assumed to have same access frequencies into a > region. As long as the assumption (pages in a region have same access > frequencies) is kept, only one page in the region is required to be > checked. Therefore, the monitoring overhead is controllable by setting > the number of regions. > > Nonetheless, this scheme cannot preserve the quality of the output if > the assumption is not kept. Following commit will introduce how we can > make the guarantee with some sort of best effort. > > Signed-off-by: SeongJae Park <sjpark@xxxxxxxxx> > --- Reviewed-by: Leonard Foerster <foersleo@xxxxxxxxx>
