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*参照元 [#oafea5f0] #backlinks *説明 [#b50a9d0c] -パス: [[linux-4.4.1/mm/migrate.c]] -FIXME: これは何？ --説明 **引数 [#m80800a0] -struct page *page -- --[[linux-4.4.1/page]] -struct page *newpage -- --[[linux-4.4.1/page]] -int force -- -enum migrate_mode mode -- --[[linux-4.4.1/migrate_mode]] **返り値 [#hdf102b3] -int -- **参考 [#n757ff62] *実装 [#s2357c7c] static int __unmap_and_move(struct page *page, struct page *newpage, int force, enum migrate_mode mode) { int rc = -EAGAIN; int page_was_mapped = 0; struct anon_vma *anon_vma = NULL; - --[[linux-4.4.1/anon_vma]] if (!trylock_page(page)) { if (!force || mode == MIGRATE_ASYNC) goto out; - --[[linux-4.4.1/trylock_page()]] /* * It's not safe for direct compaction to call lock_page. * For example, during page readahead pages are added locked * to the LRU. Later, when the IO completes the pages are * marked uptodate and unlocked. However, the queueing * could be merging multiple pages for one bio (e.g. * mpage_readpages). If an allocation happens for the * second or third page, the process can end up locking * the same page twice and deadlocking. Rather than * trying to be clever about what pages can be locked, * avoid the use of lock_page for direct compaction * altogether. */ if (current->flags & PF_MEMALLOC) goto out; lock_page(page); - --[[linux-4.4.1/lock_page()]] } if (PageWriteback(page)) { /* * Only in the case of a full synchronous migration is it * necessary to wait for PageWriteback. In the async case, * the retry loop is too short and in the sync-light case, * the overhead of stalling is too much */ if (mode != MIGRATE_SYNC) { rc = -EBUSY; goto out_unlock; } if (!force) goto out_unlock; wait_on_page_writeback(page); - --[[linux-4.4.1/PageWriteback()]] --[[linux-4.4.1/wait_on_page_writeback()]] } /* * By try_to_unmap(), page->mapcount goes down to 0 here. In this case, * we cannot notice that anon_vma is freed while we migrates a page. * This get_anon_vma() delays freeing anon_vma pointer until the end * of migration. File cache pages are no problem because of page_lock() * File Caches may use write_page() or lock_page() in migration, then, * just care Anon page here. * * Only page_get_anon_vma() understands the subtleties of * getting a hold on an anon_vma from outside one of its mms. * But if we cannot get anon_vma, then we won't need it anyway, * because that implies that the anon page is no longer mapped * (and cannot be remapped so long as we hold the page lock). */ if (PageAnon(page) && !PageKsm(page)) anon_vma = page_get_anon_vma(page); - --[[linux-4.4.1/PageAnon()]] --[[linux-4.4.1/PageKsm()]] --[[linux-4.4.1/page_get_anon_vma()]] /* * Block others from accessing the new page when we get around to * establishing additional references. We are usually the only one * holding a reference to newpage at this point. We used to have a BUG * here if trylock_page(newpage) fails, but would like to allow for * cases where there might be a race with the previous use of newpage. * This is much like races on refcount of oldpage: just don't BUG(). */ if (unlikely(!trylock_page(newpage))) goto out_unlock; if (unlikely(isolated_balloon_page(page))) { /* * A ballooned page does not need any special attention from * physical to virtual reverse mapping procedures. * Skip any attempt to unmap PTEs or to remap swap cache, * in order to avoid burning cycles at rmap level, and perform * the page migration right away (proteced by page lock). */ rc = balloon_page_migrate(newpage, page, mode); goto out_unlock_both; } - --[[linux-4.4.1/isolated_balloon_page()]] --[[linux-4.4.1/balloon_page_migrate()]] /* * Corner case handling: * 1. When a new swap-cache page is read into, it is added to the LRU * and treated as swapcache but it has no rmap yet. * Calling try_to_unmap() against a page->mapping==NULL page will * trigger a BUG. So handle it here. * 2. An orphaned page (see truncate_complete_page) might have * fs-private metadata. The page can be picked up due to memory * offlining. Everywhere else except page reclaim, the page is * invisible to the vm, so the page can not be migrated. So try to * free the metadata, so the page can be freed. */ if (!page->mapping) { VM_BUG_ON_PAGE(PageAnon(page), page); if (page_has_private(page)) { try_to_free_buffers(page); goto out_unlock_both; } - --[[linux-4.4.1/VM_BUG_ON_PAGE()]] --[[linux-4.4.1/PageAnon()]] --[[linux-4.4.1/page_has_private()]] --[[linux-4.4.1/try_to_free_buffers()]] } else if (page_mapped(page)) { /* Establish migration ptes */ VM_BUG_ON_PAGE(PageAnon(page) && !PageKsm(page) && !anon_vma, page); try_to_unmap(page, TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS); page_was_mapped = 1; - --[[linux-4.4.1/VM_BUG_ON_PAGE()]] --[[linux-4.4.1/PageAnon()]] --[[linux-4.4.1/PageKsm()]] --[[linux-4.4.1/try_to_unmap()]] } if (!page_mapped(page)) rc = move_to_new_page(newpage, page, mode); - --[[linux-4.4.1/page_mapped()]] --[[linux-4.4.1/move_to_new_page()]] if (page_was_mapped) remove_migration_ptes(page, rc == MIGRATEPAGE_SUCCESS ? newpage : page); - --[[linux-4.4.1/remove_migration_ptes()]] out_unlock_both: unlock_page(newpage); - --[[linux-4.4.1/unlock_page()]] out_unlock: /* Drop an anon_vma reference if we took one */ if (anon_vma) put_anon_vma(anon_vma); unlock_page(page); - --[[linux-4.4.1/put_anon_vma()]] out: return rc; } *コメント [#v18242a2]
