On Mon 26-08-19 22:35:08, Pankaj Suryawanshi wrote: > On Mon, Aug 26, 2019 at 12:34 PM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > > On Thu 22-08-19 23:54:19, Pankaj Suryawanshi wrote: > > > 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 are just a way to group physically contiguous pages. They > > just exist along with the physically contiguous memory. The migrate type > > for most of the memory is set to MIGRATE_MOVABLE. Portion of the memory > > might be reserved by CMA then that memory has MIGRATE_CMA. Following > > set_pageblock_migratetype call paths will give you a good picture. > > it means if i have 4096 continuous pages = 1 pageblock > then all the 4096 pages of same type. but if any one page is different than > block type then ? it changed the block type or something else ? That really depends on the specific migrate type. CMA, ISOLATE migrate types are all or nothing IIRC. I would have to check the code to tell exactly when MOVABLE/UNMOVABLE pageblocks transitions are done. steal_suitable_fallback sounds like a good start to look at. -- Michal Hocko SUSE Labs
