linux-kernel - [RFC PATCH 6/6] mm: remove now-unused mmdrop

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Message-Id: <20201016024019.1882062-7-jannh@google.com>
Date:   Fri, 16 Oct 2020 04:40:19 +0200
From:   Jann Horn <jannh@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Eric Biederman <ebiederm@...ssion.com>,
        Oleg Nesterov <oleg@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Will Deacon <will@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: [RFC PATCH 6/6] mm: remove now-unused mmdrop_async()

The preceding patches have removed all users of mmdrop_async(); get rid of
it.

Note that on MMU, we still need async_put_work because mmput_async() uses
it, which in turn is used by binder's shrinker callback. We could claw back
those 4 words per mm if we made mmput_async() depend on
CONFIG_ANDROID_BINDER_IPC.

Signed-off-by: Jann Horn <jannh@...gle.com>
---
 include/linux/mm_types.h |  2 ++
 kernel/fork.c            | 16 ----------------
 2 files changed, 2 insertions(+), 16 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 764d251966c7..8fde2068bde1 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -560,7 +560,9 @@ struct mm_struct {
 #ifdef CONFIG_HUGETLB_PAGE
 		atomic_long_t hugetlb_usage;
 #endif
+#ifdef CONFIG_MMU
 		struct work_struct async_put_work;
+#endif
 	} __randomize_layout;
 
 	/*
diff --git a/kernel/fork.c b/kernel/fork.c
index 4383bf055b40..c5f2ec544933 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -666,22 +666,6 @@ void __mmdrop(struct mm_struct *mm)
 }
 EXPORT_SYMBOL_GPL(__mmdrop);
 
-static void mmdrop_async_fn(struct work_struct *work)
-{
-	struct mm_struct *mm;
-
-	mm = container_of(work, struct mm_struct, async_put_work);
-	__mmdrop(mm);
-}
-
-static void mmdrop_async(struct mm_struct *mm)
-{
-	if (unlikely(atomic_dec_and_test(&mm->mm_count))) {
-		INIT_WORK(&mm->async_put_work, mmdrop_async_fn);
-		schedule_work(&mm->async_put_work);
-	}
-}
-
 static inline void free_signal_struct(struct signal_struct *sig)
 {
 	taskstats_tgid_free(sig);
-- 
2.29.0.rc1.297.gfa9743e501-goog