From mboxrd@z Thu Jan 1 00:00:00 1970 From: Minchan Kim Subject: Re: [PATCH v9] mm: support madvise(MADV_FREE) Date: Fri, 4 Jul 2014 15:41:02 +0900 Message-ID: <20140704064102.GH2939@bbox> References: <1404174975-22019-1-git-send-email-minchan@kernel.org> <20140701145058.GA2084@node.dhcp.inet.fi> <20140703010318.GA2939@bbox> <20140703072954.GC2939@bbox> <20140703102901.322bfdb0@mschwide> <20140703083729.GE2939@bbox> <20140703180100.5f24a139@mschwide> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Return-path: Content-Disposition: inline In-Reply-To: <20140703180100.5f24a139@mschwide> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Martin Schwidefsky Cc: "Kirill A. Shutemov" , Andrew Morton , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Michael Kerrisk , Linux API , Hugh Dickins , Johannes Weiner , Rik van Riel , KOSAKI Motohiro , Mel Gorman , Jason Evans , Zhang Yanfei , Heiko Carstens , linux390-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org, Gerald Schaefer List-Id: linux-api@vger.kernel.org Hello, On Thu, Jul 03, 2014 at 06:01:00PM +0200, Martin Schwidefsky wrote: > On Thu, 3 Jul 2014 17:37:29 +0900 > Minchan Kim wrote: > > > Hello, > > > > On Thu, Jul 03, 2014 at 10:29:01AM +0200, Martin Schwidefsky wrote: > > > On Thu, 3 Jul 2014 16:29:54 +0900 > > > Minchan Kim wrote: > > > > > > > Hello, > > > > > > > > On Thu, Jul 03, 2014 at 10:03:19AM +0900, Minchan Kim wrote: > > > > > Hello, > > > > > > > > > > On Tue, Jul 01, 2014 at 05:50:58PM +0300, Kirill A. Shutemov wrote: > > > > > > On Tue, Jul 01, 2014 at 09:36:15AM +0900, Minchan Kim wrote: > > > > > > > + do { > > > > > > > + /* > > > > > > > + * XXX: We can optimize with supporting Hugepage free > > > > > > > + * if the range covers. > > > > > > > + */ > > > > > > > + next = pmd_addr_end(addr, end); > > > > > > > + if (pmd_trans_huge(*pmd)) > > > > > > > + split_huge_page_pmd(vma, addr, pmd); > > > > > > > > > > > > Could you implement proper THP support before upstreaming the feature? > > > > > > It shouldn't be a big deal. > > > > > > > > > > Okay, Hope to review. > > > > > > > > > > Thanks for the feedback! > > > > > > > > > > > > > I tried to implement it but had a issue. > > > > > > > > I need pmd_mkold, pmd_mkclean for MADV_FREE operation and pmd_dirty for > > > > page_referenced. When I investigate all of arches supported THP, > > > > it's not a big deal but s390 is not sure to me who has no idea of > > > > soft tracking of s390 by storage key instead of page table information. > > > > Cced s390 maintainer. Hope to help. > > > > > > Storage key for dirty and referenced tracking is a thing of the past. > > > The current code for s390 uses software tracking for dirty and referenced. > > > There is one catch though, for ptes the software implementation covers > > > dirty and referenced bit but for pmds only referenced bit is available. > > > The reason is that there is no free bit left in the pmd entry for the > > > software dirty bit. > > > > Thanks for the quick reply. > > > > > > > > > So, if there isn't any help from s390, I should introduce > > > > HAVE_ARCH_THP_MADVFREE to disable MADV_FREE support of THP in s390 but > > > > not want to introduce such new config. > > > > > > Why is the dirty bit for pmds needed for the MADV_FREE implementation? > > > > MADV_FREE semantic want it. > > > > When madvise syscall is called, VM clears dirty bit of ptes of > > the range. If memory pressure happens, VM checks dirty bit of > > page table and if it found still "clean", it means it's a > > "lazyfree pages" so VM could discard the page instead of swapping out. > > Once there was store operation for the page before VM peek a page > > to reclaim, dirty bit is set so VM can swap out the page instead of > > discarding to keep up-to-date contents. > > > > If it's hard on s390, maybe we could use just reference bit > > instead of dirty bit to check recent access but it might change > > semantic a bit with other OSes. :( > > Just discussed this with Gerald and we found a trick how we can add > a dirty bit to the pmd entries. That will be a non-trivial patch but > we can do it. Until that time you could just define pmd_dirty to > always return true and the code should "work" in the sense that it > does not break anything. Will work. I will post a patch when I finish the work. Hope to review. Thanks for your advise! > > -- > blue skies, > Martin. > > "Reality continues to ruin my life." - Calvin. > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo-Bw31MaZKKs0EbZ0PF+XxCw@public.gmane.org For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org -- Kind regards, Minchan Kim