On Wed, 11 Jan 2012 17:41:26 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > On Wed, 11 Jan 2012 12:23:11 +0400 > Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx> wrote: > > > KAMEZAWA Hiroyuki wrote: > > > On Fri, 06 Jan 2012 21:38:56 +0400 > > > Konstantin Khlebnikov<khlebnikov@xxxxxxxxxx> wrote: > > > > > >> Memory migration fill pte with migration entry and it didn't update rss counters. > > >> Then it replace migration entry with new page (or old one if migration was failed). > > >> But between this two passes this pte can be unmaped, or task can fork child and > > >> it will get copy of this migration entry. Nobody account this into rss counters. > > >> > > >> This patch properly adjust rss counters for migration entries in zap_pte_range() > > >> and copy_one_pte(). Thus we avoid extra atomic operations on migration fast-path. > > >> > > >> Signed-off-by: Konstantin Khlebnikov<khlebnikov@xxxxxxxxxx> > > > > > > It's better to show wheter this is a bug-fix or not in changelog. > > > > > > IIUC, the bug-fix is the 1st harf of this patch + patch [2/3]. > > > Your new bug-check code is in patch[1/3] and 2nd half of this patch. > > > > > > > No, there only one new bug-check in 1st patch, this is non-fatal warning. > > I didn't hide this check under CONFIG_VM_DEBUG because it rather small and > > rss counters covers whole page-table management, this is very good invariant. > > Currently I can trigger this warning only on this rare race -- extremely loaded > > memory compaction catches this every several seconds. > > > > 1/3 bug-check > > 2/3 fix preparation > > 3/3 bugfix in two places: > > do rss++ in copy_one_pte() > > do rss-- in zap_pte_range() > > > > Hmm, ok, I read wrong. > > So, I think you should post the patch with [BUGFIX] and > report 'what happens' and 'what is the bug' , 'what you fixed' explicitly. > > As... > == > This patch series fixes per-mm rss counter accounting bug. When pages are > heavily migrated, the rss counters will go wrong by fork() and unmap() > because they ignores migration_pte_entries. > This rarelly happens but will make rss counter incorrect. > > This seires of patches will fix the issue by adding proper accounting of > migration_pte_entries in unmap() and fork(). This series includes > bug check code, too. Putting "fix" in the patch title text is a good way of handling this. I renamed [3/3] to "mm: fix rss count leakage during migration" and shall queue it for 3.3. If people think we should also backport it into -stable then please let me know. I reordered the patches and worked the chagnelogs quite a bit. I now have: : From: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx> : Subject: mm: fix rss count leakage during migration : : Memory migration fills a pte with a migration entry and it doesn't update : the rss counters. Then it replaces the migration entry with the new page : (or the old one if migration failed). But between these two passes this : pte can be unmaped, or a task can fork a child and it will get a copy of : this migration entry. Nobody accounts for this in the rss counters. : : This patch properly adjust rss counters for migration entries in : zap_pte_range() and copy_one_pte(). Thus we avoid extra atomic operations : on the migration fast-path. : : Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx> : Cc: Hugh Dickins <hughd@xxxxxxxxxx> : Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> and : From: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx> : Subject: mm: add rss counters consistency check : : Warn about non-zero rss counters at final mmdrop. : : This check will prevent reoccurences of bugs such as that fixed in "mm: : fix rss count leakage during migration". : : I didn't hide this check under CONFIG_VM_DEBUG because it rather small and : rss counters cover whole page-table management, so this is a good : invariant. : : Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx> : Cc: Hugh Dickins <hughd@xxxxxxxxxx> : Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> and : From: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx> : Subject: mm: postpone migrated page mapping reset : : Postpone resetting page->mapping until the final remove_migration_ptes(). : Otherwise the expression PageAnon(migration_entry_to_page(entry)) does not : work. : : Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx> : Cc: Hugh Dickins <hughd@xxxxxxxxxx> : Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>