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Date: Fri, 17 Feb 2017 11:15:32 -0500 From: Johannes Weiner <hannes@...xchg.org> To: Minchan Kim <minchan@...nel.org> Cc: Shaohua Li <shli@...com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, Kernel-team@...com, mhocko@...e.com, hughd@...gle.com, riel@...hat.com, mgorman@...hsingularity.net, akpm@...ux-foundation.org Subject: Re: [PATCH V3 3/7] mm: reclaim MADV_FREE pages On Fri, Feb 17, 2017 at 02:41:08PM +0900, Minchan Kim wrote: > Hi Johannes, > > On Thu, Feb 16, 2017 at 01:40:18PM -0500, Johannes Weiner wrote: > > On Tue, Feb 14, 2017 at 11:36:09AM -0800, Shaohua Li wrote: > > > @@ -911,7 +911,7 @@ static void page_check_dirty_writeback(struct page *page, > > > * Anonymous pages are not handled by flushers and must be written > > > * from reclaim context. Do not stall reclaim based on them > > > */ > > > - if (!page_is_file_cache(page)) { > > > + if (!page_is_file_cache(page) || page_is_lazyfree(page)) { > > > > Do we need this? MADV_FREE clears the dirty bit off the page; we could > > just let them go through with the function without any special-casing. > > I thought some driver potentially can do GUP with FOLL_TOUCH so that the > lazyfree page can have PG_dirty with !PG_swapbacked. In this case, > throttling logic of shrink_page_list can be confused? Yep, agreed. We should filter these pages here. > > > @@ -1142,7 +1144,7 @@ static unsigned long shrink_page_list(struct list_head *page_list, > > > * The page is mapped into the page tables of one or more > > > * processes. Try to unmap it here. > > > */ > > > - if (page_mapped(page) && mapping) { > > > + if (page_mapped(page) && (mapping || lazyfree)) { > > > > Do we actually need to filter for mapping || lazyfree? If we fail to > > allocate swap, we don't reach here. If the page is a truncated file > > page, ttu returns pretty much instantly with SWAP_AGAIN. We should be > > able to just check for page_mapped() alone, no? > > try_to_unmap_one assumes every anonymous pages reached will have swp_entry > so it should be changed to check PageSwapCache if we go to the way. Yep, I think it should check page_mapping(). To me that would make the most sense, see other email: "Don't unmap a ram page with valid data when there is no secondary storage mapping to maintain integrity."
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