On Mon, Nov 22, 2010 at 09:01:32PM -0800, Andrew Morton wrote: > On Tue, 23 Nov 2010 13:52:05 +0900 Minchan Kim <minchan.kim@xxxxxxxxx> wrote: > > > >> +/* > > >> + * Function used to forecefully demote a page to the head of the inactive > > >> + * list. > > >> + */ > > > > > > This comment is wrong? __The page gets moved to the _tail_ of the > > > inactive list? > > > > No. I add it in _head_ of the inactive list intentionally. > > Why I don't add it to _tail_ is that I don't want to be aggressive. > > The page might be real working set. So I want to give a chance to > > activate it again. > > Well.. why? The user just tried to toss the page away altogether. If > the kernel wasn't able to do that immediately, the best it can do is to > toss the page away asap? > I'm just guessing here on the motivation but maybe it is in case FADV_DONENEED was called on a page in use by another process (via read/write more do than being mapped). Process A says "I don't need this" but by moving it to the head of the list we give Process B a chance to reference it and reactivate without incurring a major fault? > > If it's not working set, it can be reclaimed easily and it can prevent > > active page demotion since inactive list size would be big enough for > > not calling shrink_active_list. > > What is "working set"? Mapped and unmapped pagecache, or are you > referring solely to mapped pagecache? > > If it's mapped pagecache then the user was being a bit silly (or didn't > know that some other process had mapped the file). In which case we > need to decide what to do - leave the page alone, deactivate it, or > half-deactivate it as this patch does. > What are the odds of an fadvise() user having used mincore() in advance to determine if the page was in use by another process? I would guess "low" so this half-deactivate gives a chance for the page to be promoted again as well as a chance for the flusher threads to clean the page if it really is to be reclaimed. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- 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/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>