Lines Matching refs:the
4 Page migration allows the moving of the physical location of pages between
5 nodes in a numa system while the process is running. This means that the
6 virtual addresses that the process sees do not change. However, the
7 system rearranges the physical location of those pages.
9 The main intend of page migration is to reduce the latency of memory access
10 by moving pages near to the processor where the process accessing that memory
13 Page migration allows a process to manually relocate the node on which its
14 pages are located through the MF_MOVE and MF_MOVE_ALL options while setting
16 from another process using the sys_migrate_pages() function call. The
18 process that are located on the from nodes to the destination nodes.
19 Page migration functions are provided by the numactl package by Andi Kleen
23 migration. cat /proc/<pid>/numa_maps allows an easy review of where the
24 pages of a process are located. See also the numa_maps documentation in the
27 Manual migration is useful if for example the scheduler has relocated
29 administrator may detect the situation and move the pages of the process
30 nearer to the new processor. The kernel itself does only provide
33 "move_pages" allows the moving of individual pages within a process.
35 accesses and may use the result to move pages to more advantageous
38 Larger installations usually partition the system using cpusets into
39 sections of nodes. Paul Jackson has equipped cpusets with the ability to
42 Cpusets allows the automation of process locality. If a task is moved to
43 a new cpuset then also all its pages are moved with it so that the
44 performance of the process does not sink dramatically. Also the pages
45 of processes in a cpuset are moved if the allowed memory nodes of a
48 Page migration allows the preservation of the relative location of pages
51 process. This is necessary in order to preserve the memory latencies.
55 description for those trying to use migrate_pages() from the kernel
56 (for userspace usage see the Andi Kleen's numactl package mentioned above)
57 and then a low level description of how the low level details work.
62 1. Remove pages from the LRU.
67 Calling isolate_lru_page increases the references to the page
68 so that it cannot vanish while the page migration occurs.
69 It also prevents the swapper or other scans to encounter
70 the page.
74 how to allocate the correct new page given the old page.
77 to do the migration. It will call the function to allocate
78 the new page for each page that is considered for
85 if all references to a page are removable at the time. The page has
86 already been removed from the LRU via isolate_lru_page() and the refcount
87 is increased so that the page cannot be freed while page migration occurs.
91 1. Lock the page to be migrated
95 3. Prep the new page that we want to move to. It is locked
96 and set to not being uptodate so that all accesses to the new
97 page immediately lock while the move is in progress.
99 4. The new page is prepped with some settings from the old page so that
100 accesses to the new page will discover a page with the correct settings.
102 5. All the page table references to the page are converted
104 This decrease the mapcount of a page. If the resulting
105 mapcount is not zero then we do not migrate the page.
106 All user space processes that attempt to access the page
107 will now wait on the page lock.
110 to access the page via the mapping to block on the radix tree spinlock.
112 7. The refcount of the page is examined and we back out if references remain
113 otherwise we know that we are the only one referencing this page.
115 8. The radix tree is checked and if it does not contain the pointer to this
116 page then we back out because someone else modified the radix tree.
118 9. The radix tree is changed to point to the new page.
120 10. The reference count of the old page is dropped because the radix tree
121 reference is gone. A reference to the new page is established because
122 the new page is referenced to by the radix tree.
124 11. The radix tree lock is dropped. With that lookups in the mapping
125 become possible again. Processes will move from spinning on the tree_lock
126 to sleeping on the locked new page.
128 12. The page contents are copied to the new page.
130 13. The remaining page flags are copied to the new page.
132 14. The old page flags are cleared to indicate that the page does
135 15. Queued up writeback on the new page is triggered.
139 the page lock.
141 19. The page locks are dropped from the old and new page.
142 Processes waiting on the page lock will redo their page faults
143 and will reach the new page.
145 20. The new page is moved to the LRU and can be scanned by the swapper