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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1780410367; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=aaCCVm5RLQadoWEaT8DmWxpLPBnStemVS7Mt3XQQms8=; b=L2RI+gNBcMGevj0O6kgQ8FIn4IwANqNs7GPGJG7QXneLD7ooNbxp4zZf0UOO7jAR9KTg7Z zNaXOQctDLp+OunulhuUgj4mGHRL+FTZd+xBL8ALS6Ar0on4DhVaxoJMO8JS94nFh7dvBh 1rwDuKvlYpDaQ63Xla/iDQVnDe6zH2w= From: Usama Arif To: Andrew Morton , david@kernel.org, chrisl@kernel.org, kasong@tencent.com, ljs@kernel.org, ziy@nvidia.com Cc: ying.huang@linux.alibaba.com, Baoquan He , willy@infradead.org, youngjun.park@lge.com, hannes@cmpxchg.org, riel@surriel.com, shakeel.butt@linux.dev, alex@ghiti.fr, kas@kernel.org, baohua@kernel.org, dev.jain@arm.com, baolin.wang@linux.alibaba.com, npache@redhat.com, Liam R. Howlett , ryan.roberts@arm.com, Vlastimil Babka , lance.yang@linux.dev, linux-kernel@vger.kernel.org, nphamcs@gmail.com, shikemeng@huaweicloud.com, kernel-team@meta.com, Usama Arif Subject: [v2 02/16] mm: extract mm_prepare_for_swap_entries() helper Date: Tue, 2 Jun 2026 07:24:10 -0700 Message-ID: <20260602142537.198755-3-usama.arif@linux.dev> In-Reply-To: <20260602142537.198755-1-usama.arif@linux.dev> References: <20260602142537.198755-1-usama.arif@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT When a swap entry is installed in a page table, the mm must be added to init_mm.mmlist so that swapoff can find and unuse its swap entries. This double-checked locking pattern is currently open-coded in try_to_unmap_one() and copy_nonpresent_pte(). Move it into mm_prepare_for_swap_entries() in mm/internal.h and convert both callers so it can be reused by upcoming PMD-level swap entry code paths that also need to register the mm with swapoff. copy_nonpresent_pte() previously inserted into &src_mm->mmlist rather than &init_mm.mmlist, but the insertion point is irrelevant, mmlist is a circular list and swapoff walks it entirely from init_mm.mmlist, so only membership matters, not position. Reviewed-by: Dev Jain Signed-off-by: Usama Arif --- mm/internal.h | 13 +++++++++++++ mm/memory.c | 9 +-------- mm/rmap.c | 7 +------ 3 files changed, 15 insertions(+), 14 deletions(-) diff --git a/mm/internal.h b/mm/internal.h index 181e79f1d6a2..ace2f8ef1d35 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -1951,4 +1951,17 @@ static inline int get_sysctl_max_map_count(void) bool may_expand_vm(struct mm_struct *mm, const vma_flags_t *vma_flags, unsigned long npages); +/* + * Ensure @mm is on the init_mm.mmlist so swapoff can find it. + */ +static inline void mm_prepare_for_swap_entries(struct mm_struct *mm) +{ + if (list_empty(&mm->mmlist)) { + spin_lock(&mmlist_lock); + if (list_empty(&mm->mmlist)) + list_add(&mm->mmlist, &init_mm.mmlist); + spin_unlock(&mmlist_lock); + } +} + #endif /* __MM_INTERNAL_H */ diff --git a/mm/memory.c b/mm/memory.c index 56be920c56d7..137f34c3fd32 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -953,14 +953,7 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm, if (swap_dup_entry_direct(entry) < 0) return -EIO; - /* make sure dst_mm is on swapoff's mmlist. */ - if (unlikely(list_empty(&dst_mm->mmlist))) { - spin_lock(&mmlist_lock); - if (list_empty(&dst_mm->mmlist)) - list_add(&dst_mm->mmlist, - &src_mm->mmlist); - spin_unlock(&mmlist_lock); - } + mm_prepare_for_swap_entries(dst_mm); /* Mark the swap entry as shared. */ if (pte_swp_exclusive(orig_pte)) { pte = pte_swp_clear_exclusive(orig_pte); diff --git a/mm/rmap.c b/mm/rmap.c index 1c77d5dc06e9..b93caabd186f 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -2304,12 +2304,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, set_pte_at(mm, address, pvmw.pte, pteval); goto walk_abort; } - if (list_empty(&mm->mmlist)) { - spin_lock(&mmlist_lock); - if (list_empty(&mm->mmlist)) - list_add(&mm->mmlist, &init_mm.mmlist); - spin_unlock(&mmlist_lock); - } + mm_prepare_for_swap_entries(mm); dec_mm_counter(mm, MM_ANONPAGES); inc_mm_counter(mm, MM_SWAPENTS); swp_pte = swp_entry_to_pte(entry); -- 2.52.0