On Tue, Nov 21, 2017 at 7:32 AM, Johannes Weiner <hannes@xxxxxxxxxxx> wrote: > On Sat, Nov 04, 2017 at 03:43:12PM -0700, Shakeel Butt wrote: >> When a thread mlocks an address space backed by file, a new >> page is allocated (assuming file page is not in memory), added >> to the local pagevec (lru_add_pvec), I/O is triggered and the >> thread then sleeps on the page. On I/O completion, the thread >> can wake on a different CPU, the mlock syscall will then sets >> the PageMlocked() bit of the page but will not be able to put >> that page in unevictable LRU as the page is on the pagevec of >> a different CPU. Even on drain, that page will go to evictable >> LRU because the PageMlocked() bit is not checked on pagevec >> drain. >> >> The page will eventually go to right LRU on reclaim but the >> LRU stats will remain skewed for a long time. >> >> However, this issue does not happen for anon pages on swap >> because unlike file pages, anon pages are not added to pagevec >> until they have been fully swapped in. > > How so? __read_swap_cache_async() is the core function that allocates > the page, and that always puts the page on the pagevec before IO is > initiated. > >> Also the fault handler uses vm_flags to set the PageMlocked() bit of >> such anon pages even before returning to mlock() syscall and mlocked >> pages will skip pagevecs and directly be put into unevictable LRU. > > Where does the swap fault path set PageMlocked()? > > I might just be missing something. No, you are right. I got confused by lru_cache_add_active_or_unevictable() in do_swap_page() but missed the preceding comment that says "ksm created a completely new copy". I will fix the the commit message as well. -- 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>
