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Thu, 18 Jun 2026 02:48:57 -0700 (PDT) From: Wang Lian To: sj@kernel.org, akpm@linux-foundation.org Cc: npache@redhat.com, gutierrez.asier@huawei-partners.com, daichaobing@sangfor.com.cn, linux-mm@kvack.org, linux-kernel@vger.kernel.org, lianux.mm@gmail.com, kunwu.chan@gmail.com Subject: [RFC PATCH 3/6] mm/damon/vaddr: implement mTHP-aware DAMOS_COLLAPSE handler Date: Thu, 18 Jun 2026 17:48:35 +0800 Message-ID: <20260618094838.32805-4-lianux.mm@gmail.com> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20260618094838.32805-1-lianux.mm@gmail.com> References: <20260618094838.32805-1-lianux.mm@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org 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: Wang Lian --- mm/damon/vaddr.c | 38 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 38 insertions(+) diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c index d27147603564..2a3757c13bf0 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 +900,40 @@ 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 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); + + mm = damon_get_mm(target); + if (!mm) + return 0; + + while (addr < end) { + ret = damon_collapse_folio_range(mm, addr, target_order); + if (!ret) + applied += chunk_sz; + *sz_filter_passed += chunk_sz; + 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 +957,9 @@ 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: -- 2.50.1 (Apple Git-155)