Re: PageBlocks and Migrate Types
On Mon 26-08-19 22:35:08, Pankaj Suryawanshi wrote: > On Mon, Aug 26, 2019 at 12:34 PM Michal Hocko wrote: > > > > On Thu 22-08-19 23:54:19, Pankaj Suryawanshi wrote: > > > On Thu, Aug 22, 2019 at 6:22 PM Michal Hocko 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
Re: PageBlocks and Migrate Types
On Thu 22-08-19 23:54:19, Pankaj Suryawanshi wrote: > On Thu, Aug 22, 2019 at 6:22 PM Michal Hocko 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. > Pageblocks and its type dynamically changes ? Yes as the purpose of the underlying memory for the block changes. -- Michal Hocko SUSE Labs
Re: PageBlocks and Migrate Types
On Thu, Aug 22, 2019 at 6:22 PM Michal Hocko 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_$TYPE > to see how it is used in the code. > > > How many movable/unmovable pages are defined by default? > > There is nothing like that. It depends on how many objects of a specific > type are allocated. It means that it started creating pageblocks after allocation of different objects, but from which block it allocate initially when there is nothing like pageblocks ? (when memory subsystem up) Pageblocks and its type dynamically changes ? > > > HTH > -- > Michal Hocko > SUSE Labs
Re: PageBlocks and Migrate Types
On Wed 21-08-19 22:23:44, Pankaj Suryawanshi wrote: > Hello, > > 1. What are Pageblocks and migrate types(MIGRATE_CMA) in Linux memory ? Pageblocks are a simple grouping of physically contiguous pages with common set of flags. I haven't checked closely recently so I might misremember but my recollection is that only the migrate type is stored there. Normally we would store that information into page flags but there is not enough room there. MIGRATE_CMA represent pages allocated for the CMA allocator. There are other migrate types denoting unmovable/movable allocations or pages that are isolated from the page allocator. Very broadly speaking, the migrate type groups pages with similar movability properties to reduce fragmentation that compaction cannot do anything about because there are objects of different properties around. Please note that pageblock might contain objects of a different migrate type in some cases (e.g. low on memory). Have a look at gfpflags_to_migratetype and how the gfp mask is converted to a migratetype for the allocation. Also follow different MIGRATE_$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
