On Mon, Sep 23, 2013 at 04:19:36PM +0800, Weijie Yang wrote: > This patch series fix a few bugs in mm/zswap based on Linux-3.11. > > v2 --> v3 > - keep GFP_KERNEL flag Why do you drop this? It's plain BUG. I read Bob's reply but it couldn't justify to let the pain remain. First of all, let's fix it and better idea could come later. > > v1 --> v2 > - free memory in zswap_frontswap_invalidate_area(in patch 1) > - fix whitespace corruption (line wrapping) > > Corresponding mail thread: https://lkml.org/lkml/2013/8/18/59 > > These issues fixed/optimized are: > > 1. memory leaks when re-swapon > > 2. memory leaks when invalidate and reclaim occur concurrently > > 3. avoid unnecessary page scanning > > > Issues discussed in that mail thread NOT fixed as it happens rarely or > not a big problem or controversial: > > 1. a "theoretical race condition" when reclaim page > When a handle alloced from zbud, zbud considers this handle is used > validly by upper(zswap) and can be a candidate for reclaim. But zswap has > to initialize it such as setting swapentry and adding it to rbtree. > so there is a race condition, such as: > thread 0: obtain handle x from zbud_alloc > thread 1: zbud_reclaim_page is called > thread 1: callback zswap_writeback_entry to reclaim handle x > thread 1: get swpentry from handle x (it is random value now) > thread 1: bad thing may happen > thread 0: initialize handle x with swapentry > > 2. frontswap_map bitmap not cleared after zswap reclaim > Frontswap uses frontswap_map bitmap to track page in "backend" implementation, > when zswap reclaim a page, the corresponding bitmap record is not cleared. > > 3. the potential that zswap store and reclaim functions called recursively > > > mm/zswap.c | 28 ++++++++++++++++++++-------- > 1 file changed, 20 insertions(+), 8 deletions(-) > > -- > 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> -- Kind regards, Minchan Kim -- 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>