On Tue, 15 Dec 2020 12:54:36 +0100 SeongJae Park <[email protected]> wrote:
> From: SeongJae Park <[email protected]> > > Even somehow the initial monitoring target regions are well constructed > to fulfill the assumption (pages in same region have similar access > frequencies), the data access pattern can be dynamically changed. This > will result in low monitoring quality. To keep the assumption as much > as possible, DAMON adaptively merges and splits each region based on > their access frequency. > > For each ``aggregation interval``, it compares the access frequencies of > adjacent regions and merges those if the frequency difference is small. > Then, after it reports and clears the aggregated access frequency of > each region, it splits each region into two or three regions if the > total number of regions will not exceed the user-specified maximum > number of regions after the split. > > In this way, DAMON provides its best-effort quality and minimal overhead > while keeping the upper-bound overhead that users set. > > Signed-off-by: SeongJae Park <[email protected]> > Reviewed-by: Leonard Foerster <[email protected]> > --- > include/linux/damon.h | 41 +++++--- > mm/damon/core.c | 220 ++++++++++++++++++++++++++++++++++++++++-- > 2 files changed, 240 insertions(+), 21 deletions(-) > [...] > diff --git a/mm/damon/core.c b/mm/damon/core.c > index 167487e75737..0f9beb60d9dd 100644 > --- a/mm/damon/core.c > +++ b/mm/damon/core.c [...] > + > +/* > + * Split a region in two > + * > + * r the region to be split > + * sz_r size of the first sub-region that will be made > + */ > +static void damon_split_region_at(struct damon_ctx *ctx, > + struct damon_region *r, unsigned long sz_r) > +{ > + struct damon_region *new; > + > + new = damon_new_region(r->ar.start + sz_r, r->ar.end); Coverity Static Analysis Security Testing (SAST) by Synopsys, Inc. found that 'damon_new_region()' could return NULL in case of memory allocation failure, but NULL check for 'new' is missed here. I will add the check in the next version. > + r->ar.end = new->ar.start; > + > + damon_insert_region(new, r, damon_next_region(r)); > +} [...] Thanks, SeongJae Park
