Can contigmalloc(9) fail even when M_NOWAIT is *not* specified?

[Pratyush Yadav]

Hi,

The contigmalloc() function does not sleep waiting for memory resources
to be freed up, but instead actively reclaims pages before giving up.
However, unless M_NOWAIT is specified, it may select a page for reclama-
tion that must first be written to backing storage, causing it to sleep.

So if M_NOWAIT is *not* specified, can contigmalloc() "give up", and
return NULL?

[Conrad Meyer]

Yes.

Post by Pratyush Yadav
Hi,

The contigmalloc() function does not sleep waiting for memory resources
to be freed up, but instead actively reclaims pages before giving up.
However, unless M_NOWAIT is specified, it may select a page for reclama-
tion that must first be written to backing storage, causing it to sleep.

So if M_NOWAIT is *not* specified, can contigmalloc() "give up", and
return NULL?
--
Regards,
Pratyush Yadav
_______________________________________________
https://lists.freebsd.org/mailman/listinfo/freebsd-hackers

[Andriy Gapon]

Post by Pratyush Yadav
Hi,

The contigmalloc() function does not sleep waiting for memory resources
to be freed up, but instead actively reclaims pages before giving up.
However, unless M_NOWAIT is specified, it may select a page for reclama-
tion that must first be written to backing storage, causing it to sleep.

So if M_NOWAIT is *not* specified, can contigmalloc() "give up", and
return NULL?

Yes.

[O'Connor, Daniel]

Post by Pratyush Yadav
Hi,

The contigmalloc() function does not sleep waiting for memory resources
to be freed up, but instead actively reclaims pages before giving up.
However, unless M_NOWAIT is specified, it may select a page for reclama-
tion that must first be written to backing storage, causing it to sleep.

So if M_NOWAIT is *not* specified, can contigmalloc() "give up", and
return NULL?

Yes.

This seems pretty surprising to me.. Perhaps the man page could have a warning about it - right now it fairly strongly implies that !M_NOWAIT will wait forever.

--
Daniel O'Connor
"The nice thing about standards is that there
are so many of them to choose from."
-- Andrew Tanenbaum