On Mon, Sep 26, 2011 at 05:59:39PM +0530, kautuk.c @samsung.com wrote: > On Mon, Sep 26, 2011 at 5:40 PM, kautuk.c @samsung.com > <consul.kautuk@xxxxxxxxx> wrote: > > On Mon, Sep 26, 2011 at 4:59 PM, Johannes Weiner <jweiner@xxxxxxxxxx> wrote: > >> On Sun, Sep 25, 2011 at 04:29:40PM +0530, Kautuk Consul wrote: > >>> write_scan_unavictable_node checks the value req returned by > >>> strict_strtoul and returns 1 if req is 0. > >>> > >>> However, when strict_strtoul returns 0, it means successful conversion > >>> of buf to unsigned long. > >>> > >>> Due to this, the function was not proceeding to scan the zones for > >>> unevictable pages even though we write a valid value to the > >>> scan_unevictable_pages sys file. > >> > >> Given that there is not a real reason for this knob (anymore) and that > >> it apparently never really worked since the day it was introduced, how > >> about we just drop all that code instead? > >> > >> Hannes > >> > >> --- > >> From: Johannes Weiner <jweiner@xxxxxxxxxx> > >> Subject: mm: remove sysctl to manually rescue unevictable pages > >> > >> At one point, anonymous pages were supposed to go on the unevictable > >> list when no swap space was configured, and the idea was to manually > >> rescue those pages after adding swap and making them evictable again. > >> But nowadays, swap-backed pages on the anon LRU list are not scanned > >> without available swap space anyway, so there is no point in moving > >> them to a separate list anymore. > > > > Is this code only for anonymous pages ? > > It seems to look at all pages in the zone both file as well as anon. > > > >> > >> The manual rescue could also be used in case pages were stranded on > >> the unevictable list due to race conditions. But the code has been > >> around for a while now and newly discovered bugs should be properly > >> reported and dealt with instead of relying on such a manual fixup. > > > > What you say seems to be all right for anon pages, but what about file > > pages ? > > I'm not sure about how this could happen, but what if some file-system caused > > a file cache page to be set to evictable or reclaimable without > > actually removing > > that page from the unevictable list ? > > What I would like to also add is that while the transition of an anon > page from and > to the unevictable lists is straight-forward, should we make the same assumption > about file cache pages ? We should make no assumptions if our code base is open source :-) > I am not sure about this, but could a file-system cause this kind of a problem > independent of the mlocking behaviour of a user-mode app ? Currently, I only see shmem and ramfs meddling with unevictability outside of mlock and they both look correct to me. I'd say that if a filesystem required this knob and user-intervention for the VM to behave correctly, it needs fixing. -- 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>