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b=SpAiFJPcWumzD9KUnk4LIR5Dx1RgP30kUnv/949Qg4Z7M7bmOz+XsdkwxIDXRevbv HJ7okfgYwgEdHbF4B4JOU0D3Iiurwg/f3vNNkD4VIE8c7hJ+kOKY+RkFphuKHx6M2n Ml8B8RoTqArrzuNGEmUgASaIKhZl8GMjNuz+gemb6AZpnmTry012Rgxw/xmUykJBeY Kua4nATj7VxPSDtZAzNQGoyXN2qydoIZzCx1SyV9zLbDgR93DVsyfACSji314wsrFc UZvZw76SrM/MWpMn3DPNq0HhyVcnw90NZWIOThRlljQkacEQGvmWa+DWPRm6qlO0eh o2gpt/qUgetag== Message-ID: Date: Wed, 25 Feb 2026 14:44:01 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-unstable v1 3/5] mm/khugepaged: define COLLAPSE_MAX_PTES_LIMIT as HPAGE_PMD_NR - 1 To: Nico Pache Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, aarcange@redhat.com, akpm@linux-foundation.org, anshuman.khandual@arm.com, apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, byungchul@sk.com, catalin.marinas@arm.com, cl@gentwo.org, corbet@lwn.net, dave.hansen@linux.intel.com, dev.jain@arm.com, gourry@gourry.net, hannes@cmpxchg.org, hughd@google.com, jackmanb@google.com, jack@suse.cz, jannh@google.com, jglisse@google.com, joshua.hahnjy@gmail.com, kas@kernel.org, lance.yang@linux.dev, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, mhiramat@kernel.org, mhocko@suse.com, peterx@redhat.com, pfalcato@suse.de, rakie.kim@sk.com, raquini@redhat.com, rdunlap@infradead.org, richard.weiyang@gmail.com, rientjes@google.com, rostedt@goodmis.org, rppt@kernel.org, ryan.roberts@arm.com, shivankg@amd.com, sunnanyong@huawei.com, surenb@google.com, thomas.hellstrom@linux.intel.com, tiwai@suse.de, usamaarif642@gmail.com, vbabka@suse.cz, vishal.moola@gmail.com, wangkefeng.wang@huawei.com, will@kernel.org, willy@infradead.org, yang@os.amperecomputing.com, ying.huang@linux.alibaba.com, ziy@nvidia.com, zokeefe@google.com References: <20260212021835.17755-1-npache@redhat.com> <20260212021835.17755-4-npache@redhat.com> <493d7898-c959-42ee-ad09-35ffc631ec21@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Stat-Signature: 3oy8hmb1fnh8jx4zd4ikpwc4yyoqkear X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 00C0BC0007 X-HE-Tag: 1772027056-350867 X-HE-Meta: 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 xKBSUgEG o1KqUGAgSUGj3Uj9wk2/evUeSZCJW+nRJKPhbB2RqTYPC5V4dSf5xHpYsBTjBtBl0Gm3S3Ee3FHs4qPM= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2/25/26 01:35, Nico Pache wrote: > On Thu, Feb 12, 2026 at 12:51 PM David Hildenbrand (Arm) > wrote: >> >> On 2/12/26 03:18, Nico Pache wrote: >>> The value (HPAGE_PMD_NR - 1) is used often in the khugepaged code to >>> signify the limit of the max_ptes_* values. Add a define for this to >>> increase code readability and reuse. >>> >>> Signed-off-by: Nico Pache >>> --- >>> mm/khugepaged.c | 15 ++++++++------- >>> 1 file changed, 8 insertions(+), 7 deletions(-) >>> >>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >>> index c362b3b2e08a..3dcce6018f20 100644 >>> --- a/mm/khugepaged.c >>> +++ b/mm/khugepaged.c >>> @@ -85,6 +85,7 @@ static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait); >>> * >>> * Note that these are only respected if collapse was initiated by khugepaged. >>> */ >>> +#define COLLAPSE_MAX_PTES_LIMIT (HPAGE_PMD_NR - 1) >>> unsigned int khugepaged_max_ptes_none __read_mostly; >>> static unsigned int khugepaged_max_ptes_swap __read_mostly; >>> static unsigned int khugepaged_max_ptes_shared __read_mostly; >>> @@ -252,7 +253,7 @@ static ssize_t max_ptes_none_store(struct kobject *kobj, >>> unsigned long max_ptes_none; >>> >>> err = kstrtoul(buf, 10, &max_ptes_none); >>> - if (err || max_ptes_none > HPAGE_PMD_NR - 1) >>> + if (err || max_ptes_none > COLLAPSE_MAX_PTES_LIMIT) >>> return -EINVAL; >>> >>> khugepaged_max_ptes_none = max_ptes_none; >>> @@ -277,7 +278,7 @@ static ssize_t max_ptes_swap_store(struct kobject *kobj, >>> unsigned long max_ptes_swap; >>> >>> err = kstrtoul(buf, 10, &max_ptes_swap); >>> - if (err || max_ptes_swap > HPAGE_PMD_NR - 1) >>> + if (err || max_ptes_swap > COLLAPSE_MAX_PTES_LIMIT) >>> return -EINVAL; >>> >>> khugepaged_max_ptes_swap = max_ptes_swap; >>> @@ -303,7 +304,7 @@ static ssize_t max_ptes_shared_store(struct kobject *kobj, >>> unsigned long max_ptes_shared; >>> >>> err = kstrtoul(buf, 10, &max_ptes_shared); >>> - if (err || max_ptes_shared > HPAGE_PMD_NR - 1) >>> + if (err || max_ptes_shared > COLLAPSE_MAX_PTES_LIMIT) >>> return -EINVAL; >>> >>> khugepaged_max_ptes_shared = max_ptes_shared; >>> @@ -384,7 +385,7 @@ int __init khugepaged_init(void) >>> return -ENOMEM; >>> >>> khugepaged_pages_to_scan = HPAGE_PMD_NR * 8; >>> - khugepaged_max_ptes_none = HPAGE_PMD_NR - 1; >>> + khugepaged_max_ptes_none = COLLAPSE_MAX_PTES_LIMIT; >>> khugepaged_max_ptes_swap = HPAGE_PMD_NR / 8; >>> khugepaged_max_ptes_shared = HPAGE_PMD_NR / 2; >> >> >> Changing these is ok. I don't like the name either. > > Yeah I prefer COLLAPSE_MAX_PTES as others suggested, its shorter and > more general. > COLLAPSE_MAX_PTES is misleading. We will happily collapse for 512 PTEs. It's all about khugepaged_max_ptes_* semantics. >> >> It should be clear that they all belong to the "khugepaged_max_ptes" * >> values. (see below) >> >>> >>> @@ -1869,7 +1870,7 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr, >>> bool is_shmem = shmem_file(file); >>> >>> VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem); >>> - VM_BUG_ON(start & (HPAGE_PMD_NR - 1)); >>> + VM_BUG_ON(start & (COLLAPSE_MAX_PTES_LIMIT)); >>> >>> result = alloc_charge_folio(&new_folio, mm, cc); >>> if (result != SCAN_SUCCEED) >>> @@ -2209,7 +2210,7 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr, >>> * unwritten page. >>> */ >>> folio_mark_uptodate(new_folio); >>> - folio_ref_add(new_folio, HPAGE_PMD_NR - 1); >>> + folio_ref_add(new_folio, COLLAPSE_MAX_PTES_LIMIT); >>> >>> if (is_shmem) >>> folio_mark_dirty(new_folio); >>> @@ -2303,7 +2304,7 @@ static enum scan_result hpage_collapse_scan_file(struct mm_struct *mm, unsigned >>> memset(cc->node_load, 0, sizeof(cc->node_load)); >>> nodes_clear(cc->alloc_nmask); >>> rcu_read_lock(); >>> - xas_for_each(&xas, folio, start + HPAGE_PMD_NR - 1) { >>> + xas_for_each(&xas, folio, start + COLLAPSE_MAX_PTES_LIMIT) { >>> if (xas_retry(&xas, folio)) >>> continue; >>> >> >> Changing these is not. They are semantically something different. > > With the new name these are ok right? given we dropped the LIMIT > aspect. The only thing that comes to mind is that COLLAPSE_MAX_PTES > would seemingly refer to 512 not 511, but I'm ok with that if no one > objects. Just leave it at HPAGE_PMD_NR - 1, any magical constant will make this code only more confusing. -- Cheers, David