On Thu, 23 Apr 2026 14:57:34 -0400 Peter Xu <[email protected]> wrote:
> On Thu, Apr 23, 2026 at 07:08:00PM +0100, Kiryl Shutsemau wrote: > > On Thu, Apr 23, 2026 at 10:50:06AM -0400, Peter Xu wrote: [...] > > > - Whether we have explored other approaches on page hotness tracking [...] > > DAMON is built around sampling. It is good for working set estimation, > > but I don't think it is directly useful for eviction decision. It can > > miss hot pages. LRU rotation will also loose info. > > Exactly. If we need to collect ACCESS bit (or anything similar) for > eviction accuracy pusrpose, IIUC we need per-page info, we can't estimate > by sampling. That's a fair argument. Nonetheless, there are some companies who use DAMON [1] for a similar eviction purpose on their products. Also, page level accuracy issue was indeed concerns from many people. DAMON therefore provides page level DAMOS filter [2]. The idea is finding a large region of cold pages in low overhead first, then do page level access recheck on page of the region using the filter, just before doing the eviction. DAMON-based memory tiering also uses it [3], to avoid wrongly promoting/demoting cold/hot pages in DAMON-claimed hot/cold regions. The evaluation result was not very bad, and a few more users reported positive test results. Also, DAMON can be used for page level monitoring [5] and open to changes for users. Actually a work [6] for making DAMON-based page level monitoring more lightweight is ongoing. I understand no one fits all and the decision is up to each user :) Nevertheless, I will be happy to help if you have any question or request for DAMON. [1] https://cdn.amazon.science/ee/a4/41ff11374f2f865e5e24de11bd17/resource-management-in-aurora-serverless.pdf [2] https://origin.kernel.org/doc/html/latest/mm/damon/design.html#filters [3] https://github.com/damonitor/damo/blob/next/scripts/mem_tier.sh#L40 [4] https://www.phoronix.com/news/DAMON-Self-Tuned-Memory-Tiering [5] https://origin.kernel.org/doc/html/latest/mm/damon/faq.html#can-i-simply-monitor-page-granularity [6] https://lore.kernel.org/[email protected] Thanks, SJ [...]
