This patch adds new system call sys_vrange.
NAME
vrange - give pin/unpin hint for kernel to help reclaim.
SYNOPSIS
int vrange(unsigned_long start, size_t length, int mode, int behavior);
DESCRIPTOIN
Applications can use vrange(2) to advise the kernel how it should
handle paging I/O in this VM area. The idea is to help the kernel
discard pages of vrange instead of reclaiming when memory pressure
happens. It means kernel doesn't discard any pages of vrange if ther is
no memory pressure.
mode:
VRANGE_VOLATILE
hint to kernel so VM can discard in vrange pages when
memory pressure happens.
VRANGE_NOVOLATILE
hint to kernel so VM doesn't discard vrange pages
any more.
behavior:
VRANGE_FULL_MODE
Once VM start to discard pages, it discards all pages
in a vrange.
VRANGE_PARTIAL_MODE
VM discards some pages of all vranges by round-robin
return values:
If user try to access purged memory without VRANGE_NOVOLATILE call,
he can encounter SIGBUS if the page was discarded by kernel.
RETURN VALUE
On success vrange returns zero or 1. zero means kernel doesn't discard
any pages on [start, start + length). 1 means kernel did discard
one of pages on the range.
ERRORS
EINVAL This error can occur for the following reasons:
* The value length is negative.
* addr is not page-aligned
* mode or behavior are not a vaild value.
ENOMEM Not enough memory
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
arch/x86/syscalls/syscall_64.tbl | 1 +
include/uapi/asm-generic/mman-common.h | 5 +++
mm/vrange.c | 58 ++++++++++++++++++++++++++++++++++
3 files changed, 64 insertions(+)
diff --git a/arch/x86/syscalls/syscall_64.tbl b/arch/x86/syscalls/syscall_64.tbl
index 38ae65d..dc332bd 100644
--- a/arch/x86/syscalls/syscall_64.tbl
+++ b/arch/x86/syscalls/syscall_64.tbl
@@ -320,6 +320,7 @@
311 64 process_vm_writev sys_process_vm_writev
312 common kcmp sys_kcmp
313 common finit_module sys_finit_module
+314 common vrange sys_vrange
#
# x32-specific system call numbers start at 512 to avoid cache impact
diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
index 4164529..736696e 100644
--- a/include/uapi/asm-generic/mman-common.h
+++ b/include/uapi/asm-generic/mman-common.h
@@ -66,4 +66,9 @@
#define MAP_HUGE_SHIFT 26
#define MAP_HUGE_MASK 0x3f
+#define VRANGE_VOLATILE 0 /* unpin all pages so VM can discard them */
+#define VRANGE_NOVOLATILE 1 /* pin all pages so VM can't discard them */
+
+#define VRANGE_FULL_MODE 0 /* discard all pages of the range */
+#define VRANGE_PARTIAL_MODE 1 /* discard a few pages of the range */
#endif /* __ASM_GENERIC_MMAN_COMMON_H */
diff --git a/mm/vrange.c b/mm/vrange.c
index e265c82..2f77d89 100644
--- a/mm/vrange.c
+++ b/mm/vrange.c
@@ -4,6 +4,8 @@
#include <linux/vrange.h>
#include <linux/slab.h>
+#include <linux/syscalls.h>
+#include <linux/mman.h>
static struct kmem_cache *vrange_cachep;
@@ -155,3 +157,59 @@ void exit_vrange(struct mm_struct *mm)
free_vrange(range);
}
}
+
+/*
+ * The vrange(2) system call.
+ *
+ * Applications can use vrange() to advise the kernel how it should
+ * handle paging I/O in this VM area. The idea is to help the kernel
+ * discard pages of vrange instead of swapping out when memory pressure
+ * happens. The information provided is advisory only, and can be safely
+ * disregarded by the kernel if system has enough free memory.
+ *
+ * mode values:
+ * VRANGE_VOLATILE - hint to kernel so VM can discard vrange pages when
+ * memory pressure happens.
+ * VRANGE_NOVOLATILE - hint to kernel so VM doesn't discard vrange pages
+ * any more.
+ * behavior values:
+ *
+ * VRANGE_FULL_MODE - Once VM start to discard pages, it discards all pages
+ * in a vrange.
+ * VRANGE_PARTIAL_MODE - VM discards some pages of all vranges by round-robin
+ *
+ * return values:
+ * 0 - success and NOT purged.
+ * 1 - at least, one of pages [start, start + len) is discarded by VM.
+ * -EINVAL - start len < 0, start is not page-aligned, start is greater
+ * than TASK_SIZE or "mode" is not a valid value.
+ * -ENOMEM - Short of free memory in system for successful system call.
+ */
+SYSCALL_DEFINE4(vrange, unsigned long, start,
+ size_t, len, int, mode, int, behavior)
+{
+ unsigned long end;
+ struct mm_struct *mm = current->mm;
+ int ret = -EINVAL;
+
+ if (start & ~PAGE_MASK)
+ goto out;
+
+ len &= PAGE_MASK;
+ if (!len)
+ goto out;
+
+ end = start len;
+ if (end < start)
+ goto out;
+
+ if (start >= TASK_SIZE)
+ goto out;
+
+ if (mode == VRANGE_VOLATILE)
+ ret = add_vrange(mm, start, end - 1);
+ else if (mode == VRANGE_NOVOLATILE)
+ ret = remove_vrange(mm, start, end - 1);
+out:
+ return ret;
+}
--
1.8.1.1
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>