On Tue, Oct 08, 2013 at 01:08:53PM -0700, Andrew Morton wrote: > On Tue, 08 Oct 2013 10:13:20 +0200 Krzysztof Kozlowski <k.kozlowski@xxxxxxxxxxx> wrote: > > > On pon, 2013-10-07 at 15:03 -0700, Andrew Morton wrote: > > > On Mon, 07 Oct 2013 17:25:41 +0200 Krzysztof Kozlowski <k.kozlowski@xxxxxxxxxxx> wrote: > > > > > > > During swapoff the frontswap_map was NULL-ified before calling > > > > frontswap_invalidate_area(). However the frontswap_invalidate_area() > > > > exits early if frontswap_map is NULL. Invalidate was never called during > > > > swapoff. > > > > > > > > This patch moves frontswap_map_set() in swapoff just after calling > > > > frontswap_invalidate_area() so outside of locks > > > > (swap_lock and swap_info_struct->lock). This shouldn't be a problem as > > > > during swapon the frontswap_map_set() is called also outside of any > > > > locks. > > > > > > > > > > Ahem. So there's a bunch of code in __frontswap_invalidate_area() > > > which hasn't ever been executed and nobody noticed it. So perhaps that > > > code isn't actually needed? > > > > > > More seriously, this patch looks like it enables code which hasn't been > > > used or tested before. How well tested was this? > > > > > > Are there any runtime-visible effects from this change? > > > > I tested zswap on x86 and x86-64 and there was no difference. This is > > good as there shouldn't be visible anything because swapoff is unusing > > all pages anyway: > > try_to_unuse(type, false, 0); /* force all pages to be unused */ > > > > I haven't tested other frontswap users. > > So is that code in __frontswap_invalidate_area() unneeded? Yes, to expand on what Bob said, __frontswap_invalidate_area() is still needed to let any frontswap backend free per-swaptype resources. __frontswap_invalidate_area() is _not_ for freeing structures associated with individual swapped out pages since all of the pages should be brought back into memory by try_to_unuse() before __frontswap_invalidate_area() is called. The reason we never noticed this for zswap is that zswap has no dynamically allocated per-type resources. In the expected case, where all of the pages have been drained from zswap, zswap_frontswap_invalidate_area() is a no-op. Seth -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>