From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 9 Feb 2006 21:39:25 -0800 (PST) From: Christoph Lameter Subject: Minor updates for page migration Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: akpm@osdl.org Cc: linux-mm@kvack.org List-ID: This adds some additional comments in order to help others figure out how exactly the code works. And fix a variable name. Also swap_page does need to ignore all reference bits when unmapping a page. Otherwise we may have to repeatedly unmap a frequently touched page. So change the try_to_unmap parameter to 1. Signed-off-by: Christoph Lameter Index: linux-2.6.16-rc2-mm1/mm/vmscan.c =================================================================== --- linux-2.6.16-rc2-mm1.orig/mm/vmscan.c 2006-02-09 20:04:37.000000000 -0800 +++ linux-2.6.16-rc2-mm1/mm/vmscan.c 2006-02-09 21:32:24.000000000 -0800 @@ -630,7 +630,7 @@ static int swap_page(struct page *page) struct address_space *mapping = page_mapping(page); if (page_mapped(page) && mapping) - if (try_to_unmap(page, 0) != SWAP_SUCCESS) + if (try_to_unmap(page, 1) != SWAP_SUCCESS) goto unlock_retry; if (PageDirty(page)) { @@ -837,7 +837,7 @@ EXPORT_SYMBOL(migrate_page); * pages are swapped out. * * The function returns after 10 attempts or if no pages - * are movable anymore because t has become empty + * are movable anymore because to has become empty * or no retryable pages exist anymore. * * Return: Number of pages not migrated when "to" ran empty. @@ -926,12 +926,21 @@ redo: goto unlock_both; if (mapping->a_ops->migratepage) { + /* + * Most pages have a mapping and most filesystems + * should provide a migration function. Anonymous + * pages are part of swap space which also has its + * own migration function. This is the most common + * path for page migration. + */ rc = mapping->a_ops->migratepage(newpage, page); goto unlock_both; } /* - * Trigger writeout if page is dirty + * Default handling if a filesystem does not provide + * a migration function. We can only migrate clean + * pages so try to write out any dirty pages first. */ if (PageDirty(page)) { switch (pageout(page, mapping)) { @@ -947,9 +956,10 @@ redo: ; /* try to migrate the page below */ } } + /* - * If we have no buffer or can release the buffer - * then do a simple migration. + * Buffers are managed in a filesystem specific way. + * We must have no buffers or drop them. */ if (!page_has_buffers(page) || try_to_release_page(page, GFP_KERNEL)) { @@ -964,6 +974,11 @@ redo: * swap them out. */ if (pass > 4) { + /* + * Persistently unable to drop buffers..... As a + * measure of last resort we fall back to + * swap_page(). + */ unlock_page(newpage); newpage = NULL; rc = swap_page(page); -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org