On Sat, Sep 04, 2010 at 08:02:27AM +0800, Andrew Morton wrote: > On Thu, 2 Sep 2010 23:34:47 +0900 > Minchan Kim <minchan.kim@xxxxxxxxx> wrote: > > > Now update_nr_listpages doesn't have a role. That's because > > lists passed is always empty just after calling migrate_pages. > > The migrate_pages cleans up page list which have failed to migrate > > before returning by aaa994b3. > > > > [PATCH] page migration: handle freeing of pages in migrate_pages() > > > > Do not leave pages on the lists passed to migrate_pages(). Seems that we will > > not need any postprocessing of pages. This will simplify the handling of > > pages by the callers of migrate_pages(). > > > > At that time, we thought we don't need any postprocessing of pages. > > But the situation is changed. The compaction need to know the number of > > failed to migrate for COMPACTPAGEFAILED stat > > > > This patch makes new rule for caller of migrate_pages to call putback_lru_pages. > > So caller need to clean up the lists so it has a chance to postprocess the pages. > > [suggested by Christoph Lameter] > > I'm having trouble predicting what the user-visible effects of this bug > might be. Just an inaccuracy in the COMPACTPAGEFAILED vm event? Right, it's an accounting fix. Before patch COMPACTPAGEFAILED will remain 0 regardless of how many migration failures. The patch does slightly add dependency for migrate_pages() to return error code properly. Before patch, migrate_pages() calls putback_lru_pages() regardless of the error code. After patch, the migrate_pages() callers will check its return value before calling putback_lru_pages(). In current code, the two conditions do seem to match: "some pages remained in the *from list" == "migrate_pages() returns an error code". Thanks, Fengguang -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>