On Tue, Nov 23, 2010 at 4:53 PM, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > On Tue, 23 Nov 2010 16:44:50 +0900 Minchan Kim <minchan.kim@xxxxxxxxx> wrote: > >> On Tue, Nov 23, 2010 at 4:15 PM, Andrew Morton >> <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: >> > On Tue, 23 Nov 2010 15:05:39 +0900 Minchan Kim <minchan.kim@xxxxxxxxx> wrote: >> > >> >> On Tue, Nov 23, 2010 at 2:48 PM, Andrew Morton >> >> >> > move it to the head of the LRU anyway. __But given that the user has >> >> >> >> >> >> Why does it move into head of LRU? >> >> >> If the page which isn't mapped doesn't have PG_referenced, it would be >> >> >> reclaimed. >> >> > >> >> > If it's dirty or under writeback it can't be reclaimed! >> >> >> >> I see your point. And it's why I add it to head of inactive list. >> > >> > But that *guarantees* that the page will get a full trip around the >> > inactive list. __And this will guarantee that potentially useful pages >> > are reclaimed before the pages which we *know* the user doesn't want! >> > Bad! >> > >> > Whereas if we queue it to the tail, it will only get that full trip if >> > reclaim happens to run before the page is cleaned. __And we just agreed >> > that reclaim isn't likely to run immediately, because pages are being >> > freed. >> > >> > So we face a choice between guaranteed eviction of potentially-useful >> > pages (which are very expensive to reestablish) versus a *possible* >> > need to move an unreclaimable page to the head of the LRU, which is >> > cheap. >> >> How about flagging SetPageReclaim when we add it to head of inactive? >> If page write is complete, end_page_writeback would move it to tail of >> inactive. > > ooh, that sounds clever. We'd want to do that for both PageDirty() and > for PageWriteback() pages. > > But if we do it for PageDirty() pages, we'd need to clear PageReclaim() > if someone reuses the page for some reason. We'll end up with pages > all over the place which have PageReclaim set. I guess we could clear > PageReclaim() in mark_page_accessed(), but that's hardly going to give > us full coverage. > > hmm. Maybe just do it for PageWriteback pages. Then userspace can do > > sync_file_range(SYNC_FILE_RANGE_WRITE); > fadvise(DONTNEED); > > and all those pages which now have PageWriteback set will also get > PageReclaim set. > > But we'd need to avoid races against end_io when setting PageReclaim > against the PageWriteback pages - if the interrupt happens while we're > setting PageReclaim, it will end up being incorrectly set. > Okay. I will see it and resend new version. Thanks for good comment, Andrew. -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href