On 2024/1/24 04:04, Prakash Sangappa wrote:
For shared memory of type SHM_HUGETLB, hugetlb pages are reserved in
shmget() call. If SHM_NORESERVE flags is specified then the hugetlb
pages are not reserved. However when the shared memory is attached
with the shmat() call the hugetlb pages are getting reserved incorrectly
for SHM_HUGETLB shared memory created with SHM_NORESERVE which is a bug.
-------------------------------
Following test shows the issue.
$cat shmhtb.c
int main()
{
int shmflags = 0660 | IPC_CREAT | SHM_HUGETLB | SHM_NORESERVE;
int shmid;
shmid = shmget(SKEY, SHMSZ, shmflags);
if (shmid < 0)
{
printf("shmat: shmget() failed, %d\n", errno);
return 1;
}
printf("After shmget()\n");
system("cat /proc/meminfo | grep -i hugepages_");
shmat(shmid, NULL, 0);
printf("\nAfter shmat()\n");
system("cat /proc/meminfo | grep -i hugepages_");
shmctl(shmid, IPC_RMID, NULL);
return 0;
}
#sysctl -w vm.nr_hugepages=20
#./shmhtb
After shmget()
HugePages_Total: 20
HugePages_Free: 20
HugePages_Rsvd: 0
HugePages_Surp: 0
After shmat()
HugePages_Total: 20
HugePages_Free: 20
HugePages_Rsvd: 5 <--
HugePages_Surp: 0
--------------------------------
Fix is to ensure that hugetlb pages are not reserved for SHM_HUGETLB shared
memory in the shmat() call.
Signed-off-by: Prakash Sangappa <prakash.sangappa@xxxxxxxxxx>
BTW, it is better to add a Fixes tag to specify which commit
that this commit aims to fix.
Acked-by: Muchun Song <muchun.song@xxxxxxxxx>
Thanks.
