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. -- 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>
