On 05/14/2020 11:59 PM, John Hubbard wrote: > On 2020-05-11 21:22, Anshuman Khandual wrote: >> Add the following new trace events which will help in validating >> migration events involving PMD based THP pages. >> >> 1. THP_PMD_MIGRATION_ENTRY_SET 2. THP_PMD_MIGRATION_ENTRY_REMOVE >> >> There are no clear method to confirm whether a THP migration >> happened with out involving it's split. These trace events along >> with PGMIGRATE_SUCCESS and PGMIGRATE_FAILURE will provide >> additional insights. After this change, >> > > > Hi Anshuman, > > It's very nice to see this work, and I think that reporting a bit > more about THP migration stats is going to make development and > performance debugging a lot more efficient (and pleasant). That is definitely one of the motivations for these events here. > > >> A single 2M THP (2K base page) when migrated >> >> 1. Without split >> >> ................ pgmigrate_success 1 pgmigrate_fail 0 >> ................ thp_pmd_migration_entry_set 1 >> thp_pmd_migration_entry_remove 1 ................ >> > > I do think we should decouple the trace event name(s) just a *little* > more, from the mechanisms used to migrate THPs. In other words, let's > report the number of THP migration successes, and name it > accordingly--rather than "set" and "remove", which are pretty > low-level and furthermore depend on today's exact code. Agreed, the events are low level and follows the implementation very closely. Hence posted as a RFC instead, as I was not very sure about these events. > > Maybe Zi Yan's recommended name is exactly right, in fact: > > THP_PMD_MIGRATION_SUCCESS Will also add another THP_PMD_MIGRATION_FAILURE even in migrate_pages() when a huge page could not be allocated and THP gets split.
