On Fri, Apr 18, 2014 at 11:26 AM, Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> wrote: > Hi Davidlohr, > > > On 04/18/2014 03:25 AM, Davidlohr Bueso wrote: >> >> So a value of 0 bytes or pages, for shmmax and shmall, respectively, >> implies unlimited memory, as opposed to disabling sysv shared memory. > > That might be a second risk: > Right now, a sysadmin can prevent sysv memory allocations with > > # sysctl kernel.shmall=0 > > After your patch is applied, this line allows unlimited allocations. Good point. I wonder if some folk may get bitten by this complete reversal the semantics of shmall==0. > Obviously my patch has the opposite problem: 64-bit wrap-arounds. I know you alluded to a case in another thread, but I couldn't quite work out from the mail you referred to whether this was really the problem. (And I assume those folks were forced to fix their set-up scripts anyway.) So, it's not clear to me whether this is a real problem. (And your patch does not worsen things from the current situation, right?) Cheers, Michael >> --- a/include/uapi/linux/shm.h >> +++ b/include/uapi/linux/shm.h >> @@ -9,14 +9,14 @@ >> /* >> * SHMMAX, SHMMNI and SHMALL are upper limits are defaults which can >> - * be increased by sysctl >> + * be modified by sysctl. By default, disable SHMMAX and SHMALL with >> + * 0 bytes, thus allowing processes to have unlimited shared memory. >> */ >> - >> -#define SHMMAX 0x2000000 /* max shared seg size (bytes) */ >> +#define SHMMAX 0 /* max shared seg size (bytes) */ >> #define SHMMIN 1 /* min shared seg size (bytes) */ >> #define SHMMNI 4096 /* max num of segs system wide */ >> #ifndef __KERNEL__ >> -#define SHMALL (SHMMAX/getpagesize()*(SHMMNI/16)) >> +#define SHMALL 0 >> #endif >> #define SHMSEG SHMMNI /* max shared segs per process */ >> > > The "#ifndef __KERNEL__" is not required: > As there is no reference to PAGE_SIZE anymore, one definition for SHMALL is > sufficient. > > > -- > Manfred -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- 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>