[PATCH] SHM_NORESERVE flags for shmget()

Add SHM_NORESERVE functionality similar to MAP_NORESERVE for shared memory
segments.

This is mainly to avoid abuse of OVERCOMMIT_ALWAYS and this flag is ignored
for OVERCOMMIT_NEVER.

Signed-off-by: Badari Pulavarty <pbadari@us.ibm.com>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 10 insertions, 1 deletions

diff --git a/include/linux/shm.h b/include/linux/shm.h
index 80113a1f60bc..a2c896ad0bef 100644
--- a/include/linux/shm.h
+++ b/include/linux/shm.h
@@ -92,6 +92,7 @@ struct shmid_kernel /* private to the kernel */
 #define SHM_DEST        01000   /* segment will be destroyed on last detach */
 #define SHM_LOCKED      02000   /* segment will not be swapped */
 #define SHM_HUGETLB     04000   /* segment will use huge TLB pages */
+#define SHM_NORESERVE   010000  /* don't check for reservations */
 
 #ifdef CONFIG_SYSVIPC
 long do_shmat(int shmid, char __user *shmaddr, int shmflg, unsigned long *addr);
diff --git a/ipc/shm.c b/ipc/shm.c
index b58c651d31ae..587d836d80d9 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -212,8 +212,16 @@ static int newseg (key_t key, int shmflg, size_t size)
                 file = hugetlb_zero_setup(size);
                 shp->mlock_user = current->user;
         } else {
+                int acctflag = VM_ACCOUNT;
+                /*
+                 * Do not allow no accounting for OVERCOMMIT_NEVER, even
+                 * if it's asked for.
+                 */
+                if  ((shmflg & SHM_NORESERVE) &&
+                                sysctl_overcommit_memory != OVERCOMMIT_NEVER)
+                        acctflag = 0;
                 sprintf (name, "SYSV%08x", key);
-                file = shmem_file_setup(name, size, VM_ACCOUNT);
+                file = shmem_file_setup(name, size, acctflag);
         }
         error = PTR_ERR(file);
         if (IS_ERR(file))