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Date:   Mon, 23 Nov 2020 21:39:42 -0800
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Subject: [PATCH 1/2] mm/madvise: allow process_madvise operations on entire
 memory range
From:   Suren Baghdasaryan <surenb@google.com>
To:     surenb@google.com
Cc:     akpm@linux-foundation.org, mhocko@kernel.org, mhocko@suse.com,
        rientjes@google.com, willy@infradead.org, hannes@cmpxchg.org,
        guro@fb.com, riel@surriel.com, minchan@kernel.org,
        christian@brauner.io, oleg@redhat.com, timmurray@google.com,
        linux-api@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, kernel-team@android.com
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Precedence: bulk

process_madvise requires a vector of address ranges to be provided for
its operations. When an advice should be applied to the entire process,
the caller process has to obtain the list of VMAs of the target process
by reading the /proc/pid/maps or some other way. The cost of this
operation grows linearly with increasing number of VMAs in the target
process. Even constructing the input vector can be non-trivial when
target process has several thousands of VMAs and the syscall is being
issued during high memory pressure period when new allocations for such
a vector would only worsen the situation.
In the case when advice is being applied to the entire memory space of
the target process, this creates an extra overhead.
Add PMADV_FLAG_RANGE flag for process_madvise enabling the caller to
advise a memory range of the target process. For now, to keep it simple,
only the entire process memory range is supported, vec and vlen inputs
in this mode are ignored and can be NULL and 0.
Instead of returning the number of bytes that advice was successfully
applied to, the syscall in this mode returns 0 on success. This is due
to the fact that the number of bytes would not be useful for the caller
that does not know the amount of memory the call is supposed to affect.
Besides, the ssize_t return type can be too small to hold the number of
bytes affected when the operation is applied to a large memory range.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 arch/alpha/include/uapi/asm/mman.h           |  4 ++
 arch/mips/include/uapi/asm/mman.h            |  4 ++
 arch/parisc/include/uapi/asm/mman.h          |  4 ++
 arch/xtensa/include/uapi/asm/mman.h          |  4 ++
 fs/io_uring.c                                |  2 +-
 include/linux/mm.h                           |  3 +-
 include/uapi/asm-generic/mman-common.h       |  4 ++
 mm/madvise.c                                 | 47 +++++++++++++++++---
 tools/include/uapi/asm-generic/mman-common.h |  4 ++
 9 files changed, 67 insertions(+), 9 deletions(-)

diff --git a/arch/alpha/include/uapi/asm/mman.h b/arch/alpha/include/uapi/asm/mman.h
index a18ec7f63888..54588d2f5406 100644
--- a/arch/alpha/include/uapi/asm/mman.h
+++ b/arch/alpha/include/uapi/asm/mman.h
@@ -79,4 +79,8 @@
 #define PKEY_ACCESS_MASK	(PKEY_DISABLE_ACCESS |\
 				 PKEY_DISABLE_WRITE)
 
+/* process_madvise flags */
+#define PMADV_FLAG_RANGE	0x1	/* advice for all VMAs in the range */
+#define PMADV_FLAG_MASK	(PMADV_FLAG_RANGE)
+
 #endif /* __ALPHA_MMAN_H__ */
diff --git a/arch/mips/include/uapi/asm/mman.h b/arch/mips/include/uapi/asm/mman.h
index 57dc2ac4f8bd..af94f38a3a9d 100644
--- a/arch/mips/include/uapi/asm/mman.h
+++ b/arch/mips/include/uapi/asm/mman.h
@@ -106,4 +106,8 @@
 #define PKEY_ACCESS_MASK	(PKEY_DISABLE_ACCESS |\
 				 PKEY_DISABLE_WRITE)
 
+/* process_madvise flags */
+#define PMADV_FLAG_RANGE	0x1	/* advice for all VMAs in the range */
+#define PMADV_FLAG_MASK	(PMADV_FLAG_RANGE)
+
 #endif /* _ASM_MMAN_H */
diff --git a/arch/parisc/include/uapi/asm/mman.h b/arch/parisc/include/uapi/asm/mman.h
index ab78cba446ed..ae644c493991 100644
--- a/arch/parisc/include/uapi/asm/mman.h
+++ b/arch/parisc/include/uapi/asm/mman.h
@@ -77,4 +77,8 @@
 #define PKEY_ACCESS_MASK	(PKEY_DISABLE_ACCESS |\
 				 PKEY_DISABLE_WRITE)
 
+/* process_madvise flags */
+#define PMADV_FLAG_RANGE	0x1	/* advice for all VMAs in the range */
+#define PMADV_FLAG_MASK	(PMADV_FLAG_RANGE)
+
 #endif /* __PARISC_MMAN_H__ */
diff --git a/arch/xtensa/include/uapi/asm/mman.h b/arch/xtensa/include/uapi/asm/mman.h
index e5e643752947..934cdd11abff 100644
--- a/arch/xtensa/include/uapi/asm/mman.h
+++ b/arch/xtensa/include/uapi/asm/mman.h
@@ -114,4 +114,8 @@
 #define PKEY_ACCESS_MASK	(PKEY_DISABLE_ACCESS |\
 				 PKEY_DISABLE_WRITE)
 
+/* process_madvise flags */
+#define PMADV_FLAG_RANGE	0x1	/* advice for all VMAs in the range */
+#define PMADV_FLAG_MASK	(PMADV_FLAG_RANGE)
+
 #endif /* _XTENSA_MMAN_H */
diff --git a/fs/io_uring.c b/fs/io_uring.c
index a8c136a1cf4e..508c48b998ee 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4118,7 +4118,7 @@ static int io_madvise(struct io_kiocb *req, bool force_nonblock)
 	if (force_nonblock)
 		return -EAGAIN;
 
-	ret = do_madvise(current->mm, ma->addr, ma->len, ma->advice);
+	ret = do_madvise(current->mm, ma->addr, ma->len, ma->advice, 0);
 	if (ret < 0)
 		req_set_fail_links(req);
 	io_req_complete(req, ret);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index db6ae4d3fb4e..414c7639e394 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2579,7 +2579,8 @@ extern int __do_munmap(struct mm_struct *, unsigned long, size_t,
 		       struct list_head *uf, bool downgrade);
 extern int do_munmap(struct mm_struct *, unsigned long, size_t,
 		     struct list_head *uf);
-extern int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int behavior);
+extern int do_madvise(struct mm_struct *mm, unsigned long start, unsigned long len_in,
+		      int behavior, unsigned int flags);
 
 #ifdef CONFIG_MMU
 extern int __mm_populate(unsigned long addr, unsigned long len,
diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
index f94f65d429be..4898034593ec 100644
--- a/include/uapi/asm-generic/mman-common.h
+++ b/include/uapi/asm-generic/mman-common.h
@@ -80,4 +80,8 @@
 #define PKEY_ACCESS_MASK	(PKEY_DISABLE_ACCESS |\
 				 PKEY_DISABLE_WRITE)
 
+/* process_madvise flags */
+#define PMADV_FLAG_RANGE	0x1	/* advice for all VMAs in the range */
+#define PMADV_FLAG_MASK	(PMADV_FLAG_RANGE)
+
 #endif /* __ASM_GENERIC_MMAN_COMMON_H */
diff --git a/mm/madvise.c b/mm/madvise.c
index a8d8d48a57fe..1aa074a46524 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -1001,6 +1001,14 @@ process_madvise_behavior_valid(int behavior)
 	}
 }
 
+static bool can_range_madv_lru_vma(struct vm_area_struct *vma, int behavior)
+{
+	if (!can_madv_lru_vma(vma))
+		return false;
+
+	return true;
+}
+
 /*
  * The madvise(2) system call.
  *
@@ -1067,15 +1075,21 @@ process_madvise_behavior_valid(int behavior)
  *  -EBADF  - map exists, but area maps something that isn't a file.
  *  -EAGAIN - a kernel resource was temporarily unavailable.
  */
-int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int behavior)
+int do_madvise(struct mm_struct *mm, unsigned long start, unsigned long len_in,
+	       int behavior, unsigned int flags)
 {
 	unsigned long end, tmp;
 	struct vm_area_struct *vma, *prev;
 	int unmapped_error = 0;
 	int error = -EINVAL;
+	int error_on_gap;
 	int write;
-	size_t len;
+	unsigned long len;
 	struct blk_plug plug;
+	bool range_madvise = !!(flags & PMADV_FLAG_RANGE);
+
+	/* For range operations gap between VMAs is normal */
+	error_on_gap = range_madvise ? 0 : -ENOMEM;
 
 	start = untagged_addr(start);
 
@@ -1123,13 +1137,14 @@ int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int beh
 	blk_start_plug(&plug);
 	for (;;) {
 		/* Still start < end. */
-		error = -ENOMEM;
+		error = error_on_gap;
+
 		if (!vma)
 			goto out;
 
 		/* Here start < (end|vma->vm_end). */
 		if (start < vma->vm_start) {
-			unmapped_error = -ENOMEM;
+			unmapped_error = error_on_gap;
 			start = vma->vm_start;
 			if (start >= end)
 				goto out;
@@ -1140,10 +1155,18 @@ int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int beh
 		if (end < tmp)
 			tmp = end;
 
+		/* For range operations skip VMAs ineligible for the behavior */
+		if (range_madvise && !can_range_madv_lru_vma(vma, behavior)) {
+			prev = vma;
+			goto skip_vma;
+		}
+
 		/* Here vma->vm_start <= start < tmp <= (end|vma->vm_end). */
 		error = madvise_vma(vma, &prev, start, tmp, behavior);
 		if (error)
 			goto out;
+
+skip_vma:
 		start = tmp;
 		if (prev && start < prev->vm_end)
 			start = prev->vm_end;
@@ -1167,7 +1190,7 @@ int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int beh
 
 SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
 {
-	return do_madvise(current->mm, start, len_in, behavior);
+	return do_madvise(current->mm, start, len_in, behavior, 0);
 }
 
 SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
@@ -1183,7 +1206,7 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
 	size_t total_len;
 	unsigned int f_flags;
 
-	if (flags != 0) {
+	if (flags & ~PMADV_FLAG_MASK) {
 		ret = -EINVAL;
 		goto out;
 	}
@@ -1216,12 +1239,21 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
 		goto release_task;
 	}
 
+	/*
+	 * For range madvise only the entire address space is supported for now
+	 * and input iovec is ignored.
+	 */
+	if (flags & PMADV_FLAG_RANGE) {
+		ret = do_madvise(mm, 0, ULONG_MAX & PAGE_MASK, behavior, flags);
+		goto release_mm;
+	}
+
 	total_len = iov_iter_count(&iter);
 
 	while (iov_iter_count(&iter)) {
 		iovec = iov_iter_iovec(&iter);
 		ret = do_madvise(mm, (unsigned long)iovec.iov_base,
-					iovec.iov_len, behavior);
+					iovec.iov_len, behavior, flags);
 		if (ret < 0)
 			break;
 		iov_iter_advance(&iter, iovec.iov_len);
@@ -1230,6 +1262,7 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
 	if (ret == 0)
 		ret = total_len - iov_iter_count(&iter);
 
+release_mm:
 	mmput(mm);
 release_task:
 	put_task_struct(task);
diff --git a/tools/include/uapi/asm-generic/mman-common.h b/tools/include/uapi/asm-generic/mman-common.h
index f94f65d429be..4898034593ec 100644
--- a/tools/include/uapi/asm-generic/mman-common.h
+++ b/tools/include/uapi/asm-generic/mman-common.h
@@ -80,4 +80,8 @@
 #define PKEY_ACCESS_MASK	(PKEY_DISABLE_ACCESS |\
 				 PKEY_DISABLE_WRITE)
 
+/* process_madvise flags */
+#define PMADV_FLAG_RANGE	0x1	/* advice for all VMAs in the range */
+#define PMADV_FLAG_MASK	(PMADV_FLAG_RANGE)
+
 #endif /* __ASM_GENERIC_MMAN_COMMON_H */
-- 
2.29.2.454.gaff20da3a2-goog