On 2014/1/16 7:15, David Rientjes wrote: > On Wed, 15 Jan 2014, Xishi Qiu wrote: > >> In the process IO direction, dio_refill_pages will call get_user_pages_fast >> to map the page from user space. If ret is less than 0 and IO is write, the >> function will create a zero page to fill data. This may work for some file >> system, but in some device operate we prefer whole write or fail, not half >> data half zero, e.g. fs metadata, like inode, identy. >> This happens often when kill a process which is doing direct IO. Consider >> the following cases, the process A is doing IO process, may enter __get_user_pages >> function, if other processes send process A SIG_KILL, A will enter the >> following branches >> /* >> * If we have a pending SIGKILL, don't keep faulting >> * pages and potentially allocating memory. >> */ >> if (unlikely(fatal_signal_pending(current))) >> return i ? i : -ERESTARTSYS; >> Return current pages. direct IO will write the pages, the subsequent pages >> which can’t get will use zero page instead. >> This patch will modify this judgment, if receive SIG_KILL, release pages and >> return an error. Direct IO will find no blocks_available and return error >> direct, rather than half IO data and half zero page. >> >> Signed-off-by: Xishi Qiu <qiuxishi@xxxxxxxxxx> >> Signed-off-by: Bin Yang <robin.yb@xxxxxxxxxx> > > It's scary to change the behavior of gup when some callers may want the > exact opposite of what you're intending here, which is sane fallback by > mapping the zero page. In fact, gup never does put_page() itself and > __get_user_pages() always returns the number of pages pinned and may not > equal what is passed. > > So, this definitely isn't the right solution for a special-case direct IO. > Instead, it would be better to code this directly in the caller and > compare the return value with nr_pages in dio_refill_pages() and then do > the put_page() itself before falling back to ZERO_PAGE(). Hi Rientjes, You are right, we should not change the behavior of gup. I have a question, if we only get a part of the pages from get_user_pages_fast(), shall we write them to the disk? or add a check before write? I'm not familiar with fs. dio_refill_pages() get_user_pages_fast() Thanks, Xishi Qiu -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
