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Thu, 02 Jul 2026 02:46:46 -0700 (PDT) Received: from localhost.localdomain ([2607:f130:0:11a::31]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-30f116065c5sm5261121eec.11.2026.07.02.02.46.44 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Thu, 02 Jul 2026 02:46:46 -0700 (PDT) From: Lian Wang To: sj@kernel.org Cc: damon@lists.linux.dev, linux-mm@kvack.org, daichaobing@sangfor.com.cn, kunwu.chan@gmail.com Subject: [RESEND RFC PATCH v2 3/5] mm/damon/vaddr: implement mTHP-aware DAMOS_COLLAPSE handler Date: Thu, 2 Jul 2026 17:46:31 +0800 Message-ID: <20260702094633.75658-4-lianux.mm@gmail.com> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20260702094633.75658-1-lianux.mm@gmail.com> References: <20260702094633.75658-1-lianux.mm@gmail.com> Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When target_order is set (non-zero), the DAMOS_COLLAPSE handler now calls damon_collapse_folio_range() to collapse pages into the requested mTHP size, iterating over the target region in order-aligned chunks. When target_order is 0 (default), the existing madvise(MADV_COLLAPSE) path is used, preserving backwards compatibility. Region boundaries are expanded outward to the covering aligned range (ALIGN_DOWN start, ALIGN end) so that collapse works even after kdamond_split_regions reduces region sizes below the chunk size. collapse_huge_page() internally validates VMA bounds, so expanding beyond the original region is safe. No external mmap lock is held: collapse_huge_page() acquires mmap_read_lock internally for validation, releases it, then acquires mmap_write_lock for the actual collapse. Holding an outer mmap_read_lock would cause a self-deadlock when the same thread attempts the inner mmap_write_lock. Co-developed-by: Kunwu Chan Signed-off-by: Kunwu Chan Signed-off-by: Lian Wang Signed-off-by: Lian Wang --- mm/damon/vaddr.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 48 insertions(+) diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c index d27147603564..98a87609376b 100644 --- a/mm/damon/vaddr.c +++ b/mm/damon/vaddr.c @@ -14,6 +14,7 @@ #include #include #include +#include #include "../internal.h" #include "ops-common.h" @@ -899,6 +900,50 @@ static unsigned long damos_va_stat(struct damon_target *target, return 0; } +static unsigned long damos_va_collapse(struct damon_target *target, + struct damon_region *r, struct damos *s, + unsigned long *sz_filter_passed) +{ + unsigned long addr, end, chunk_sz; + unsigned long last_chunk = ULONG_MAX; + unsigned int target_order = s->target_order; + unsigned long applied = 0; + struct mm_struct *mm; + int ret; + + if (target_order < 2 || target_order > HPAGE_PMD_ORDER) + return 0; + + chunk_sz = PAGE_SIZE << target_order; + addr = ALIGN_DOWN(r->ar.start, chunk_sz); + end = ALIGN(r->ar.end, chunk_sz); + if (end < addr) + return 0; + + mm = damon_get_mm(target); + if (!mm) + return 0; + + while (addr < end) { + if (addr + chunk_sz < addr) + break; + if (addr == last_chunk) + goto next; + last_chunk = addr; + + ret = damon_collapse_folio_range(mm, addr, target_order); + if (!ret) + applied += chunk_sz; + *sz_filter_passed += chunk_sz; +next: + addr += chunk_sz; + cond_resched(); + } + + mmput(mm); + return applied; +} + static unsigned long damon_va_apply_scheme(struct damon_ctx *ctx, struct damon_target *t, struct damon_region *r, struct damos *scheme, unsigned long *sz_filter_passed) @@ -922,6 +967,9 @@ static unsigned long damon_va_apply_scheme(struct damon_ctx *ctx, madv_action = MADV_NOHUGEPAGE; break; case DAMOS_COLLAPSE: + if (scheme->target_order) + return damos_va_collapse(t, r, scheme, + sz_filter_passed); madv_action = MADV_COLLAPSE; break; case DAMOS_MIGRATE_HOT: