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[79.36.127.123]) by smtp.gmail.com with ESMTPSA id j124sm21831962wmb.25.2020.04.15.02.19.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 Apr 2020 02:19:49 -0700 (PDT) Date: Wed, 15 Apr 2020 11:19:48 +0200 From: Andrea Righi To: "Huang, Ying" Cc: Andrew Morton , Minchan Kim , Anchal Agarwal , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] mm: swap: use fixed-size readahead during swapoff Message-ID: <20200415091948.GH810380@xps-13> References: <20200413111810.GA801367@xps-13> <87a73f7d71.fsf@yhuang-dev.intel.com> <20200413133150.GA810380@xps-13> <87wo6i6efn.fsf@yhuang-dev.intel.com> <20200414130520.GF810380@xps-13> <87v9m1zd83.fsf@yhuang-dev.intel.com> <20200415073239.GG810380@xps-13> <87imi1yz07.fsf@yhuang-dev.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87imi1yz07.fsf@yhuang-dev.intel.com> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Apr 15, 2020 at 03:44:08PM +0800, Huang, Ying wrote: > Andrea Righi writes: > > > mm/swapfile.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/mm/swapfile.c b/mm/swapfile.c > > index 9fd47e6f7a86..cb9eb517178d 100644 > > --- a/mm/swapfile.c > > +++ b/mm/swapfile.c > > @@ -1944,7 +1944,9 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd, > > vmf.pmd = pmd; > > last_ra = atomic_read(&last_readahead_pages); > > atomic_set(&swapin_readahead_hits, last_ra); > > You need to remove the above 2 lines firstly. Meh... too much enthusiasm, and I definitely need more coffee this morning. Here's the right patch applied: diff --git a/mm/swapfile.c b/mm/swapfile.c index 5871a2aa86a5..8b38441b66fa 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -1940,7 +1940,9 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd, vmf.vma = vma; vmf.address = addr; vmf.pmd = pmd; - page = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE, &vmf); + page = lookup_swap_cache(entry, vma, addr); + if (!page) + page = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE, &vmf); if (!page) { if (*swap_map == 0 || *swap_map == SWAP_MAP_BAD) goto try_next; And following the right results: r::swapin_nr_pages(unsigned long offset):unsigned long:$retval COUNT EVENT 1618 $retval = 1 4960 $retval = 2 41315 $retval = 4 103521 $retval = 8 swapoff time: 12.19s So, not as good as the fixed-size readahead, but it's definitely an improvement, considering that the swapoff time is ~22s without this patch applied. I think this change can be a simple and reasonable compromise. Thanks again and sorry for the noise, -Andrea