On Wed 21-08-19 22:23:44, Pankaj Suryawanshi wrote: > Hello, > > 1. What are Pageblocks and migrate types(MIGRATE_CMA) in Linux memory ? Pageblocks are a simple grouping of physically contiguous pages with common set of flags. I haven't checked closely recently so I might misremember but my recollection is that only the migrate type is stored there. Normally we would store that information into page flags but there is not enough room there. MIGRATE_CMA represent pages allocated for the CMA allocator. There are other migrate types denoting unmovable/movable allocations or pages that are isolated from the page allocator. Very broadly speaking, the migrate type groups pages with similar movability properties to reduce fragmentation that compaction cannot do anything about because there are objects of different properties around. Please note that pageblock might contain objects of a different migrate type in some cases (e.g. low on memory). Have a look at gfpflags_to_migratetype and how the gfp mask is converted to a migratetype for the allocation. Also follow different MIGRATE_$TYPE to see how it is used in the code. > How many movable/unmovable pages are defined by default? There is nothing like that. It depends on how many objects of a specific type are allocated. HTH -- Michal Hocko SUSE Labs
