From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f70.google.com (mail-pg0-f70.google.com [74.125.83.70]) by kanga.kvack.org (Postfix) with ESMTP id 2B5686B0260 for ; Wed, 11 Oct 2017 03:55:43 -0400 (EDT) Received: by mail-pg0-f70.google.com with SMTP id l24so2491417pgu.6 for ; Wed, 11 Oct 2017 00:55:43 -0700 (PDT) Received: from lgeamrelo11.lge.com (LGEAMRELO11.lge.com. [156.147.23.51]) by mx.google.com with ESMTP id e39si5040173plg.814.2017.10.11.00.55.41 for ; Wed, 11 Oct 2017 00:55:41 -0700 (PDT) Date: Wed, 11 Oct 2017 16:55:39 +0900 From: Minchan Kim Subject: Re: [PATCH -mm -v2] mm, swap: Use page-cluster as max window of VMA based swap readahead Message-ID: <20171011075539.GA5671@bbox> References: <20171011070847.16003-1-ying.huang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171011070847.16003-1-ying.huang@intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: "Huang, Ying" Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Johannes Weiner , Rik van Riel , Shaohua Li , Hugh Dickins , Fengguang Wu , Tim Chen , Dave Hansen On Wed, Oct 11, 2017 at 03:08:47PM +0800, Huang, Ying wrote: > From: Huang Ying > > When the VMA based swap readahead was introduced, a new knob > > /sys/kernel/mm/swap/vma_ra_max_order > > was added as the max window of VMA swap readahead. This is to make it > possible to use different max window for VMA based readahead and > original physical readahead. But Minchan Kim pointed out that this > will cause a regression because setting page-cluster sysctl to zero > cannot disable swap readahead with the change. > > To fix the regression, the page-cluster sysctl is used as the max > window of both the VMA based swap readahead and original physical swap > readahead. If more fine grained control is needed in the future, more > knobs can be added as the subordinate knobs of the page-cluster > sysctl. > > The vma_ra_max_order knob is deleted. Because the knob was > introduced in v4.14-rc1, and this patch is targeting being merged > before v4.14 releasing, there should be no existing users of this > newly added ABI. > > Cc: Johannes Weiner > Cc: Rik van Riel > Cc: Shaohua Li > Cc: Hugh Dickins > Cc: Fengguang Wu > Cc: Tim Chen > Cc: Dave Hansen > Reported-by: Minchan Kim > Signed-off-by: "Huang, Ying" Acked-by: Minchan Kim Below a question: > --- > Documentation/ABI/testing/sysfs-kernel-mm-swap | 10 ------- > mm/swap_state.c | 41 +++++--------------------- > 2 files changed, 7 insertions(+), 44 deletions(-) > > diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-swap b/Documentation/ABI/testing/sysfs-kernel-mm-swap > index 587db52084c7..94672016c268 100644 > --- a/Documentation/ABI/testing/sysfs-kernel-mm-swap > +++ b/Documentation/ABI/testing/sysfs-kernel-mm-swap > @@ -14,13 +14,3 @@ Description: Enable/disable VMA based swap readahead. > still used for tmpfs etc. other users. If set to > false, the global swap readahead algorithm will be > used for all swappable pages. > - > -What: /sys/kernel/mm/swap/vma_ra_max_order > -Date: August 2017 > -Contact: Linux memory management mailing list > -Description: The max readahead size in order for VMA based swap readahead > - > - VMA based swap readahead algorithm will readahead at > - most 1 << max_order pages for each readahead. The > - real readahead size for each readahead will be scaled > - according to the estimation algorithm. > diff --git a/mm/swap_state.c b/mm/swap_state.c > index ed91091d1e68..05b6803f0cce 100644 > --- a/mm/swap_state.c > +++ b/mm/swap_state.c > @@ -39,10 +39,6 @@ struct address_space *swapper_spaces[MAX_SWAPFILES]; > static unsigned int nr_swapper_spaces[MAX_SWAPFILES]; > bool swap_vma_readahead = true; > > -#define SWAP_RA_MAX_ORDER_DEFAULT 3 > - > -static int swap_ra_max_order = SWAP_RA_MAX_ORDER_DEFAULT; > - > #define SWAP_RA_WIN_SHIFT (PAGE_SHIFT / 2) > #define SWAP_RA_HITS_MASK ((1UL << SWAP_RA_WIN_SHIFT) - 1) > #define SWAP_RA_HITS_MAX SWAP_RA_HITS_MASK > @@ -664,6 +660,13 @@ struct page *swap_readahead_detect(struct vm_fault *vmf, > pte_t *tpte; > #endif > > + max_win = 1 << min_t(unsigned int, READ_ONCE(page_cluster), > + SWAP_RA_ORDER_CEILING); Why do we need READ_ONCE in here? IOW, without it, what happens? > + if (max_win == 1) { > + swap_ra->win = 1; > + return NULL; > + } -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org