On Thu, Aug 22, 2019 at 6:22 PM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > 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 properti > 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. It means that it started creating pageblocks after allocation of different objects, but from which block it allocate initially when there is nothing like pageblocks ? (when memory subsystem up) Pageblocks and its type dynamically changes ? > > > HTH > -- > Michal Hocko > SUSE Labs
