Lines Matching full:page
4 Page migration
7 Page migration allows the moving of the physical location of pages between
12 The main intend of page migration is to reduce the latency of memory access
16 Page migration allows a process to manually relocate the node on which its
22 Page migration functions are provided by the numactl package by Andi Kleen
25 which provides an interface similar to other numa functionality for page
28 proc(5) man page.
34 manual page migration support. Automatic page migration may be implemented
51 Page migration allows the preservation of the relative location of pages
57 Page migration occurs in several steps. First a high level
70 Calling isolate_lru_page increases the references to the page
71 so that it cannot vanish while the page migration occurs.
73 the page.
77 how to allocate the correct new page given the old page.
81 the new page for each page that is considered for
87 migrate_pages() does several passes over its list of pages. A page is moved
88 if all references to a page are removable at the time. The page has
90 is increased so that the page cannot be freed while page migration occurs.
94 1. Lock the page to be migrated
98 3. Lock the new page that we want to move to. It is locked so that accesses to
99 this (not yet uptodate) page immediately lock while the move is in progress.
101 4. All the page table references to the page are converted to migration
102 entries. This decreases the mapcount of a page. If the resulting
103 mapcount is not zero then we do not migrate the page. All user space
104 processes that attempt to access the page will now wait on the page lock.
107 to access the page via the mapping to block on the spinlock.
109 6. The refcount of the page is examined and we back out if references remain
110 otherwise we know that we are the only one referencing this page.
113 page then we back out because someone else modified the radix tree.
115 8. The new page is prepped with some settings from the old page so that
116 accesses to the new page will discover a page with the correct settings.
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 address space
121 reference is gone. A reference to the new page is established because
122 the new page is referenced by the address space.
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.
137 16. If migration entries were page then replace them with real ptes. Doing
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
148 Non-LRU page migration
152 for NUMA, compaction who want to create high-order page is also main customer.
163 To overclome the problem, VM supports non-LRU page migration which provides
170 1. ``bool (*isolate_page) (struct page *page, isolate_mode_t mode);``
173 if driver isolates page successfully. On returing true, VM marks the page
174 as PG_isolated so concurrent isolation in several CPUs skip the page
175 for isolation. If a driver cannot isolate the page, it should return *false*.
177 Once page is successfully isolated, VM uses page.lru fields so driver
181 | ``struct page *newpage, struct page *oldpage, enum migrate_mode);``
183 After isolation, VM calls migratepage of driver with isolated page.
184 The function of migratepage is to move content of the old page to new page
185 and set up fields of struct page newpage. Keep in mind that you should
188 MIGRATEPAGE_SUCCESS. If driver cannot migrate the page at the moment, driver
189 can return -EAGAIN. On -EAGAIN, VM will retry page migration in a short time
191 any error except -EAGAIN, VM will give up the page migration without retrying
194 Driver shouldn't touch page.lru field VM using in the functions.
196 3. ``void (*putback_page)(struct page *);``
198 If migration fails on isolated page, VM should return the isolated page
199 to the driver so VM calls driver's putback_page with migration failed page.
200 In this function, driver should put the isolated page back to the own data
203 4. non-lru movable page flags
205 There are two page flags for supporting non-lru movable page.
209 Driver should use the below function to make page movable under page_lock::
211 void __SetPageMovable(struct page *page, struct address_space *mapping)
215 PG_movable is not a real flag of struct page. Rather than, VM
216 reuses page->mapping's lower bits to represent it.
220 page->mapping = page->mapping | PAGE_MAPPING_MOVABLE;
222 so driver shouldn't access page->mapping directly. Instead, driver should
223 use page_mapping which mask off the low two bits of page->mapping under
224 page lock so it can get right struct address_space.
226 For testing of non-lru movable page, VM supports __PageMovable function.
227 However, it doesn't guarantee to identify non-lru movable page because
228 page->mapping field is unified with other variables in struct page.
229 As well, if driver releases the page after isolation by VM, page->mapping
232 page is LRU or non-lru movable once the page has been isolated. Because
233 LRU pages never can have PAGE_MAPPING_MOVABLE in page->mapping. It is also
237 For guaranteeing non-lru movable page, VM provides PageMovable function.
238 Unlike __PageMovable, PageMovable functions validates page->mapping and
240 destroying of page->mapping.
243 under page_lock before the releasing the page.
247 To prevent concurrent isolation among several CPUs, VM marks isolated page
249 movable page, it can skip it. Driver doesn't need to manipulate the flag
251 sees PG_isolated page, it means the page have been isolated by VM so it
252 shouldn't touch page.lru field.