On Tue, Nov 23, 2010 at 12:35:35PM -0800, Andrew Morton wrote: > On Tue, 23 Nov 2010 14:58:56 +0000 > Mel Gorman <mel@xxxxxxxxx> wrote: > > > On Tue, Nov 23, 2010 at 09:55:49AM -0500, Ben Gamari wrote: > > > On Tue, 23 Nov 2010 09:38:59 +0000, Mel Gorman <mel@xxxxxxxxx> wrote: > > > > > 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. > > > > > > > Do we really want to make the user jump through such hoops as using > > > mincore() just to get the kernel to handle use-once pages properly? > > > > I would think "no" which is why I support half-deactivating pages so they won't > > have to. > > If the page is page_mapped() then we can assume that some other process > is using it and we leave it alone *altogether*. > Agreed, that makes perfect sense. > If the page is dirty or under writeback (and !page_mapped()) then we > should assume that we should free it asap. The PageReclaim() trick > might help with that. > Again agreed. > I just don't see any argument for moving the page to the head of the > inactive LRU as a matter of policy. We can park it there because we > can't think of anythnig else to do with it, but it's the wrong place > for it. > Is there a better alternative? One thing that springs to mind is that we are not exactly tracking very well what effect these policy changes have. The analysis scripts I have do a reasonable job on tracking reclaim activity (although only as part of the mmtests tarball, I should split them out as a standalone tool) but not the impact - namely minor and major faults. I should sort that out so we can put better reclaim analysis in place. -- 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>