In kernel use of migrate_pages()
================================
-1. Remove pages from the LRU.
+1. Remove folios from the LRU.
- Lists of pages to be migrated are generated by scanning over
- pages and moving them into lists. This is done by
- calling isolate_lru_page().
- Calling isolate_lru_page() increases the references to the page
- so that it cannot vanish while the page migration occurs.
+ Lists of folios to be migrated are generated by scanning over
+ folios and moving them into lists. This is done by
+ calling folio_isolate_lru().
+ Calling folio_isolate_lru() increases the references to the folio
+ so that it cannot vanish while the folio migration occurs.
It also prevents the swapper or other scans from encountering
- the page.
+ the folio.
2. We need to have a function of type new_folio_t that can be
passed to migrate_pages(). This function should figure out
How migrate_pages() works
=========================
-migrate_pages() does several passes over its list of pages. A page is moved
-if all references to a page are removable at the time. The page has
-already been removed from the LRU via isolate_lru_page() and the refcount
-is increased so that the page cannot be freed while page migration occurs.
+migrate_pages() does several passes over its list of folios. A folio is moved
+if all references to a folio are removable at the time. The folio has
+already been removed from the LRU via folio_isolate_lru() and the refcount
+is increased so that the folio cannot be freed while folio migration occurs.
Steps:
(2) We want to be able to migrate unevictable folios between nodes for memory
defragmentation, workload management and memory hotplug. The Linux kernel
can only migrate folios that it can successfully isolate from the LRU
- lists (or "Movable" pages: outside of consideration here). If we were to
+ lists (or "Movable" folios: outside of consideration here). If we were to
maintain folios elsewhere than on an LRU-like list, where they can be
detected by folio_isolate_lru(), we would prevent their migration.
of VM_LOCKED VMAs that map the page (Rik van Riel had the same idea three years
earlier). But this use of the link field for a count prevented the management
of the pages on an LRU list, and thus mlocked pages were not migratable as
-isolate_lru_page() could not detect them, and the LRU list link field was not
+folio_isolate_lru() could not detect them, and the LRU list link field was not
available to the migration subsystem.
Nick resolved this by putting mlocked pages back on the LRU list before
1. 从LRU中移除页面。
- 要迁移的页面列表是通过扫描页面并把它们移到列表中来生成的。这是通过调用 isolate_lru_page()
- 来完成的。调用isolate_lru_page()增加了对该页的引用，这样在页面迁移发生时它就不会
+ 要迁移的页面列表是通过扫描页面并把它们移到列表中来生成的。这是通过调用 folio_isolate_lru()
+ 来完成的。调用folio_isolate_lru()增加了对该页的引用，这样在页面迁移发生时它就不会
消失。它还可以防止交换器或其他扫描器遇到该页。
=======================
migrate_pages()对它的页面列表进行了多次处理。如果当时对一个页面的所有引用都可以被移除，
-那么这个页面就会被移动。该页已经通过isolate_lru_page()从LRU中移除，并且refcount被
+那么这个页面就会被移动。该页已经通过folio_isolate_lru()从LRU中移除，并且refcount被
增加，以便在页面迁移发生时不释放该页。
步骤:
* ->private_lock (try_to_unmap_one)
* ->i_pages lock (try_to_unmap_one)
* ->lruvec->lru_lock (follow_page_mask->mark_page_accessed)
- * ->lruvec->lru_lock (check_pte_range->isolate_lru_page)
+ * ->lruvec->lru_lock (check_pte_range->folio_isolate_lru)
* ->private_lock (folio_remove_rmap_pte->set_page_dirty)
* ->i_pages lock (folio_remove_rmap_pte->set_page_dirty)
* bdi.wb->list_lock (folio_remove_rmap_pte->set_page_dirty)
}
EXPORT_SYMBOL(grab_cache_page_write_begin);
-bool isolate_lru_page(struct page *page)
-{
- if (WARN_RATELIMIT(PageTail(page), "trying to isolate tail page"))
- return false;
- return folio_isolate_lru((struct folio *)page);
-}
-
void putback_lru_page(struct page *page)
{
folio_putback_lru(page_folio(page));
/*
* in mm/vmscan.c:
*/
-bool isolate_lru_page(struct page *page);
bool folio_isolate_lru(struct folio *folio);
void putback_lru_page(struct page *page);
void folio_putback_lru(struct folio *folio);
}
/*
- * We can do it before isolate_lru_page because the
- * page can't be freed from under us. NOTE: PG_lock
+ * We can do it before folio_isolate_lru because the
+ * folio can't be freed from under us. NOTE: PG_lock
* is needed to serialize against split_huge_page
* when invoked from the VM.
*/
result = SCAN_FAIL;
goto xa_unlocked;
}
- /* drain lru cache to help isolate_lru_page() */
+ /* drain lru cache to help folio_isolate_lru() */
lru_add_drain();
} else if (folio_trylock(folio)) {
folio_get(folio);
page_cache_sync_readahead(mapping, &file->f_ra,
file, index,
end - index);
- /* drain lru cache to help isolate_lru_page() */
+ /* drain lru cache to help folio_isolate_lru() */
lru_add_drain();
folio = filemap_lock_folio(mapping, index);
if (IS_ERR(folio)) {
/*
* One extra ref because caller holds an extra reference, either from
- * isolate_lru_page() for a regular page, or migrate_vma_collect() for
- * a device page.
+ * folio_isolate_lru() for a regular folio, or migrate_vma_collect() for
+ * a device folio.
*/
int extra = 1 + (page == fault_page);
/*
* lru_cache_disable() needs to be called before we start compiling
- * a list of pages to be migrated using isolate_lru_page().
- * It drains pages on LRU cache and then disable on all cpus until
+ * a list of folios to be migrated using folio_isolate_lru().
+ * It drains folios on LRU cache and then disable on all cpus until
* lru_cache_enable is called.
*
* Must be paired with a call to lru_cache_enable().
projects / users / willy / xarray.git / commitdiff