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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id 88sm2089884oto.3.2021.02.26.17.31.52 (version=TLS1 cipher=ECDHE-ECDSA-AES128-SHA bits=128/128); Fri, 26 Feb 2021 17:31:53 -0800 (PST) Date: Fri, 26 Feb 2021 17:31:40 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Andrew Morton cc: Palmer Dabbelt , atishp@atishpatra.org, peterz@infradead.org, srikar@linux.vnet.ibm.com, valentin.schneider@arm.com, vbabka@suse.cz, mpe@ellerman.id.au, Palmer Dabbelt , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel-team@android.com, "Kirill A. Shutemov" Subject: Re: [PATCH 1/2] mm: Guard a use of node_reclaim_distance with CONFIFG_NUMA In-Reply-To: <20210226123716.6bc2a463e0ee9d1770c7966b@linux-foundation.org> Message-ID: References: <20210226201721.510177-1-palmer@dabbelt.com> <20210226123716.6bc2a463e0ee9d1770c7966b@linux-foundation.org> User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: B49B9E0011E0 X-Stat-Signature: 4i6k9effoz9891jay4wt8qzb5wr4j7wa Received-SPF: none (google.com>: No applicable sender policy available) receiver=imf21; identity=mailfrom; envelope-from=""; helo=mail-oo1-f50.google.com; client-ip=209.85.161.50 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1614389510-902366 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 Fri, 26 Feb 2021, Andrew Morton wrote: > On Fri, 26 Feb 2021 12:17:20 -0800 Palmer Dabbelt wrote: > > From: Palmer Dabbelt > > > > This is only useful under CONFIG_NUMA. IIUC skipping the check is the > > right thing to do here, as without CONFIG_NUMA there will never be any > > large node distances on non-NUMA systems. > > > > I expected this to manifest as a link failure under (!CONFIG_NUMA && > > CONFIG_TRANSPARENT_HUGE_PAGES), but I'm not actually seeing that. I > > think the reference is just getting pruned before it's checked, but I > > didn't get that from reading the code so I'm worried I'm missing > > something. > > > > Either way, this is necessary to guard the definition of > > node_reclaim_distance with CONFIG_NUMA. > > > > Signed-off-by: Palmer Dabbelt > > --- > > mm/khugepaged.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > > index a7d6cb912b05..b1bf191c3a54 100644 > > --- a/mm/khugepaged.c > > +++ b/mm/khugepaged.c > > @@ -819,8 +819,10 @@ static bool khugepaged_scan_abort(int nid) > > for (i = 0; i < MAX_NUMNODES; i++) { > > if (!khugepaged_node_load[i]) > > continue; > > +#ifdef CONFIG_NUMA > > if (node_distance(nid, i) > node_reclaim_distance) > > return true; > > +#endif > > } > > return false; > > } > > This makes the entire loop a no-op. Perhaps Kirill can help take a > look at removing unnecessary code in khugepaged.c when CONFIG_NUMA=n? First lines of khugepaged_scan_abort() say if (!node_reclaim_mode) return false; And include/linux/swap.h says #ifdef CONFIG_NUMA extern int node_reclaim_mode; extern int sysctl_min_unmapped_ratio; extern int sysctl_min_slab_ratio; #else #define node_reclaim_mode 0 #endif So, no need for an #ifdef CONFIG_NUMA inside khugepaged_scan_abort(). Hugh