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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-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list 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> 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 >