upstream/opnsense-src
1
0
Fork 0
mirror of https://github.com/opnsense/src.git synced 2026-06-04 06:15:33 -04:00
Code Issues Projects Releases Packages Wiki Activity Actions

buf: Make the number of pbufs slightly more dynamic

Browse source 
Various subsystems pre-allocate a set of pbufs, allocated to implement
I/O operations.  pbuf allocations are transient, unlike most buf
allocations.

Most subsystems preallocate nswbuf or nswbuf/2 pbufs each.  The
preallocation ensures that pbuf allocation will succeed in low memory
conditions, which might help avoid deadlocks.  Currently we initialize
nswbuf = min(nbuf / 4, 256).

nbuf/4 > 256 on anything but the smallest systems.  For example,
nswbuf is 256 in a VM with 128MB of memory.  In this configuration, a
firecracker VM with one CPU preallocates over 900 pbufs.  This consumes
2MB of RAM and adds several milliseconds to the kernel's (very small)
boot time.

Scale nswbuf by ncpu in the common case.  I think this makes more sense
than scaling by the amount of RAM, since pbuf allocations are transient
and aren't used for caching.  With the change, we get nswbuf=256 with 8
CPUs.  With fewer than 8 CPUs we'll preallocate fewer pbufs than before,
and with more we'll preallocate more.

Event:		BSDCan 2023
Reported by:	cperciva
Reviewed by:	glebius, kib
MFC after:	2 months
Differential Revision:	https://reviews.freebsd.org/D40216
This commit is contained in:
Mark Johnston 2023-05-30 15:11:32 -04:00
parent 7a52b570e7
commit 4e78addbef
1 changed files with 6 additions and 1 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

7
sys/kern/vfs_bio.c
View file

@ -1168,7 +1168,12 @@ kern_vfs_bio_buffer_alloc(caddr_t v, long physmem_est)
}
if (nswbuf == 0) {
nswbuf = min(nbuf / 4, 256);
/*
* Pager buffers are allocated for short periods, so scale the
* number of reserved buffers based on the number of CPUs rather
* than amount of memory.
*/
nswbuf = min(nbuf / 4, 32 * mp_ncpus);
if (nswbuf < NSWBUF_MIN)
nswbuf = NSWBUF_MIN;
}