From 418aade459f03318defd18ef0b11981a63bd81b0 Mon Sep 17 00:00:00 2001 From: Christoph Lameter Date: Fri, 10 Feb 2006 01:51:15 -0800 Subject: [PATCH] Updates for page migration 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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/vmscan.c | 25 ++++++++++++++++++++----- 1 file changed, 20 insertions(+), 5 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 5a610804cd0..5db32fdfaf3 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -632,7 +632,7 @@ 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)) { @@ -839,7 +839,7 @@ 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. @@ -928,12 +928,21 @@ 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)) { @@ -949,9 +958,10 @@ 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)) { @@ -966,6 +976,11 @@ 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); -- cgit v1.2.3-70-g09d2