On Wed, Sep 25, 2013 at 4:31 PM, Bob Liu <lliubbo@xxxxxxxxx> wrote: > On Wed, Sep 25, 2013 at 4:09 PM, Weijie Yang <weijie.yang.kh@xxxxxxxxx> wrote: >> I think I find a new issue, for integrity of this mail thread, I reply >> to this mail. >> >> It is a concurrence issue either, when duplicate store and reclaim >> concurrentlly. >> >> zswap entry x with offset A is already stored in zswap backend. >> Consider the following scenario: >> >> thread 0: reclaim entry x (get refcount, but not call zswap_get_swap_cache_page) >> >> thread 1: store new page with the same offset A, alloc a new zswap entry y. >> store finished. shrink_page_list() call __remove_mapping(), and now >> it is not in swap_cache >> > > But I don't think swap layer will call zswap with the same offset A. 1. store page of offset A in zswap 2. some time later, pagefault occur, load page data from zswap. But notice that zswap entry x is still in zswap because it is not frontswap_tmem_exclusive_gets_enabled. this page is with PageSwapCache(page) and page_private(page) = entry.val 3. change this page data, and it become dirty 4. some time later again, swap this page on the same offset A. so, a duplicate store happens. what I can think is that use flags and CAS to protect store and reclaim on the same offset happens concurrentlly. >> thread 0: zswap_get_swap_cache_page called. old page data is added to swap_cache >> >> Now, swap cache has old data rather than new data for offset A. >> error will happen If do_swap_page() get page from swap_cache. >> > > -- > Regards, > --Bob -- 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>