On Thu, 29 Dec 2011, Andrew Morton wrote: > On Wed, 28 Dec 2011 20:39:36 -0800 (PST) > Hugh Dickins <hughd@xxxxxxxxxx> wrote: > > > Replace pagevecs in putback_lru_pages() and move_active_pages_to_lru() > > by lists of pages_to_free > > One effect of the pagevec handling was to limit lru_lock hold times and > interrupt-disabled times. > > This patch removes that upper bound and has the potential to cause > various latency problems when processing large numbers of pages. > > The affected functions have rather a lot of callers. I don't think > that auditing all these callers and convincing ourselves that none of > them pass in 10,000 pages is sufficient, because that doesn't prevent us > from introducing such latency problems as the MM code evolves. That's an interesting slant on it, that hadn't crossed my mind; but it looks like intervening changes have answered that concern. putback_lru_pages() has one caller, shrink_inactive_list(); move_active_pages_to_lru() has one caller, shrink_active_list(). Following those back, they're in all cases capped to SWAP_CLUSTER_MAX pages per call. That's 32 pages, not so very much more than the 14 page limit the pagevecs were imposing. And both shrink_inactive_list() and shrink_active_list() gather these pages with isolate_lru_pages(), which does not drop lock or enable interrupts at all - probably why the SWAP_CLUSTER_MAX cap got imposed. (Don't be deceived by mm/migrate.c's putback_lru_pages()! That's a distinct function, unaffected by this patch.) Hugh -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>