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Fri, 13 Nov 2026 14:23:09 -0800 (PST) Received: from localhost ([2a03:2880:10ff:41::]) by smtp.gmail.com with ESMTPSA id 00721157ae682-8b4aa7eeaf9sm31201657b3.4.2026.11.13.14.23.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 13 Nov 2026 14:23:09 -0800 (PST) Date: Fri, 13 Nov 2026 14:23:08 -0800 From: Joshua Hahn To: "David Hildenbrand (Arm)" Cc: Hugh Dickins , Baolin Wang , Gregory Price , Zi Yan , Rakie Kim , Ying Huang , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jonathan Corbet , Shuah Khan , Randy Dunlap , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org Subject: Re: [PATCH 1/2] mm/mempolicy: merge adjacent shared policy ranges Message-ID: Mail-Followup-To: "David Hildenbrand (Arm)" , Hugh Dickins , Baolin Wang , Gregory Price , Zi Yan , Rakie Kim , Ying Huang , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jonathan Corbet , Shuah Khan , Randy Dunlap , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org References: <20261113-mempolicy_limit-v1-0-16688b2644dc@kernel.org> <20261113-mempolicy_limit-v1-1-16688b2644dc@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261113-mempolicy_limit-v1-1-16688b2644dc@kernel.org> X-Stat-Signature: 5hdyy1p6yhup3p7yotpgkc5q4htomnum X-Rspamd-Server: rspam01 X-Rspam-User: X-Spam-Status: No, score=-12.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Queue-Id: C9FD91C0006 X-HE-Tag: 1794608590-798786 X-HE-Meta: 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 apnqTp2l 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Fri, Nov 13, 2026 at 10:36:12PM +0100, David Hildenbrand (Arm) wrote: > Shared policies can retain separate tree nodes for adjacent ranges with > identical policies. This can create unnecessary policy ranges especially > when individual VMAs cover individual file ranges, and user space sets > the policy on these VMAs independently. > > Extend the existing replacement handling to merge ranges with equal policy > at either boundary. The existing replacement loop will then remove the old > nodes and installs a single node for the combined range. This also avoids > splitting an existing node when setting the same policy on a subrange. > > Extending either boundary rules out splitting an existing node, so the > allocation retry can only occur with the originally requested range. Hi David, Independent of 2/2 I think this is a really great change. Thank you! Reviewed-by: Joshua Hahn > This change will make it easier to cap the number of shared policy > ranges per inode. > > Signed-off-by: David Hildenbrand (Arm) > --- > mm/mempolicy.c | 17 +++++++++++++++++ > 1 file changed, 17 insertions(+) > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > index 06b90903e8794..183bc3bd077cd 100644 > --- a/mm/mempolicy.c > +++ b/mm/mempolicy.c > @@ -3208,6 +3208,23 @@ static int shared_policy_replace(struct shared_policy *sp, pgoff_t start, > > restart: > write_lock(&sp->lock); > + if (new) { > + /* Try to merge ranges with same policies. */ > + if (start) { > + n = sp_lookup(sp, start - 1, start); > + if (n && mpol_equal(n->policy, new->policy)) { > + new->start = n->start; > + start = new->start; > + } > + } > + if (end != ULONG_MAX) { > + n = sp_lookup(sp, end, end + 1); > + if (n && mpol_equal(n->policy, new->policy)) { > + new->end = n->end; > + end = new->end; > + } > + } > + } > n = sp_lookup(sp, start, end); > /* Take care of old policies in the same range. */ > while (n && n->start < end) { > > -- > 2.43.0 >