Michal Hocko <mhocko@xxxxxxxxxx> writes: > On Tue 12-05-20 15:14:46, Huang, Ying wrote: >> Michal Hocko <mhocko@xxxxxxxxxx> writes: >> >> > On Tue 12-05-20 14:41:46, Huang Ying wrote: >> >> To improve the code readability and get random number with higher >> >> quality. >> > >> > I understand the readability argument but why should prandom_u32_max >> > (which I was not aware of) provide a higher quality randomness? >> >> I am not expert on random number generator. I have heard about that the >> randomness of the low order bits of some random number generator isn't >> good enough. Anyway, by using the common implementation, the real >> random number generator expert can fix the possible issue once for all >> users. > > Please drop the quality argument if you cannot really justify it. This > will likely just confuse future readers the same way it confused me > here. Because prandom_u32_max uses the same source of randomness the > only difference is the way how modulo vs. u64 overflow arithmetic is > used for distributing values. I am not aware the later would be > a way to achieve a higher quality randomness. If the interval > distribution is better with the later then it would be great to have it > documented. OK. Fair enough. Best Regards, Huang, Ying >> >> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx> >> >> Cc: Michal Hocko <mhocko@xxxxxxxx> >> >> Cc: Minchan Kim <minchan@xxxxxxxxxx> >> >> Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> >> >> Cc: Hugh Dickins <hughd@xxxxxxxxxx> >> > >> > To the change itself >> > Acked-by: Michal Hocko <mhocko@xxxxxxxx> >> >> Thanks! >> >> Best Regards, >> Huang, Ying >> >> >> --- >> >> mm/swapfile.c | 2 +- >> >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> >> >> diff --git a/mm/swapfile.c b/mm/swapfile.c >> >> index a0a123e59ce6..2ec8b21201d6 100644 >> >> --- a/mm/swapfile.c >> >> +++ b/mm/swapfile.c >> >> @@ -3220,7 +3220,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) >> >> * select a random position to start with to help wear leveling >> >> * SSD >> >> */ >> >> - p->cluster_next = 1 + (prandom_u32() % p->highest_bit); >> >> + p->cluster_next = 1 + prandom_u32_max(p->highest_bit); >> >> nr_cluster = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER); >> >> >> >> cluster_info = kvcalloc(nr_cluster, sizeof(*cluster_info), >> >> -- >> >> 2.26.2
