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[2.103.239.165]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-47d192e88f5sm290811265e9.0.2025.12.24.06.08.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 Dec 2025 06:08:32 -0800 (PST) Date: Wed, 24 Dec 2025 14:08:29 +0000 From: David Laight To: Lance Yang Cc: baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, akpm@linux-foundation.org, axelrasmussen@google.com, chandna.sahil@gmail.com, chengming.zhou@linux.dev, david@kernel.org, david@redhat.com, hannes@cmpxchg.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, mhocko@suse.com, nphamcs@gmail.com, rppt@kernel.org, shakeel.butt@linux.dev, surenb@google.com, vbabka@suse.cz, weixugc@google.com, willy@infradead.org, yosry.ahmed@linux.dev, yuanchu@google.com, zhengqi.arch@bytedance.com, Lance Yang Subject: Re: [PATCH v4 1/3] mm: pagewalk: simplify hugepage boundary Message-ID: <20251224140829.2ec7bbae@pumpkin> In-Reply-To: <20251224092332.53214-1-ioworker0@gmail.com> References: <62a2d7ba-e7c3-4153-b227-c08802ca9e1c@linux.alibaba.com> <20251224092332.53214-1-ioworker0@gmail.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Wed, 24 Dec 2025 17:23:32 +0800 Lance Yang wrote: > From: Lance Yang > > > On Wed, 24 Dec 2025 15:50:34 +0800, Baolin Wang wrote: > > Hi Andrew, > > > > On 2025/11/28 15:01, Sahil Chandna wrote: > > > Replace hugepage boundary computation with ALIGN() helper instead of > > > an open coded expression. This helps to improves code readability. > > > > > > This was flagged by Coccinelle (misc/minmax.cocci) as an opportunity > > > to use min(), after which the boundary computation was updated following > > > review suggestions. > > > > > > Found by: make coccicheck MODE=report M=mm/ > > > No functional change intended. > > > > > > Acked-by: David Hildenbrand (Red Hat) > > > Suggested-by: David Hildenbrand (Red Hat) > > > Suggested-by: Matthew Wilcox > > > Suggested-by: David Laight > > > Signed-off-by: Sahil Chandna > > > --- > > > mm/pagewalk.c | 3 +-- > > > 1 file changed, 1 insertion(+), 2 deletions(-) > > > > > > diff --git a/mm/pagewalk.c b/mm/pagewalk.c > > > index 9f91cf85a5be..9fd59d517f37 100644 > > > --- a/mm/pagewalk.c > > > +++ b/mm/pagewalk.c > > > @@ -312,8 +312,7 @@ static int walk_pgd_range(unsigned long addr, unsigned long end, > > > static unsigned long hugetlb_entry_end(struct hstate *h, unsigned long addr, > > > unsigned long end) > > > { > > > - unsigned long boundary = (addr & huge_page_mask(h)) + huge_page_size(h); > > > - return boundary < end ? boundary : end; > > > + return min(ALIGN(addr, huge_page_size(h)), end); > > > } > > > > Please drop this patch from the mm-new branch, as it causes > > 'run_vmtests.sh' to hang. Specifically, it leads to the system hanging > > when executing hugepage-vmemmap test, because the program falls into an > > infinite loop in walk_hugetlb_range() and cannot break out. > > Good catch! The problem is that ALIGN() returns addr itself when already > aligned, causing the infinite loop ... Using ALIGN(addr + 1, huge_page_size(h)) would work. Although it could be (addr + 1) & ~huge_page_mask(h) which is probably the easiest to understand. Some of the 'helper' macros don't really make the code easier to read. (And that includes a lot of uses of min().) David > > > > > This patch does introduce functional changes and makes an incorrect > > assumption that the 'end' must be aligned to the hugepage size. However, > > Yep. This patch is not equivalent to the original code when addr is > already aligned :) > > > this is not necessarily the case. For example, see how pagemap_read() > > calculates the 'end': > > > > " > > end = start_vaddr + ((count / PM_ENTRY_BYTES) << PAGE_SHIFT); > > " > > > > Revert this patch, mm selftests work well.