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kboot: Allocate a really big first segment

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Allocate a huge segment for the first kexec_load segments. We limit the
lessor of:
	allocation to the size of the remaining memory segment
	45% of available memory
	95% of the memory we can allocate

This allows us to have really large RAM disks. We likely need to limit
this to the amount we actually used, though, since this can be a lot of
memory.

We have to do this complicated calculation for a few reasons: First, we
need 2 copies of the loaded kernel in the memory: The kernel can copy
everything to a temporary buffer. Next, malloc (via mmap) is limited to
a certain amount due to over commit, so we have to not allocate all we
can (only most of what we can).

Sponsored by:		Netflix
Reviewed by:		tsoome
Differential Revision:	https://reviews.freebsd.org/D38314
This commit is contained in:
Warner Losh 2023-02-03 08:41:03 -07:00
parent 1d3a7e849b
commit db8d0c0cd9
1 changed files with 16 additions and 3 deletions
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19
stand/kboot/main.c
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@ -322,6 +322,7 @@ get_phys_buffer(vm_offset_t dest, const size_t len, void **buf)
{
int i = 0;
const size_t segsize = 64*1024*1024;
size_t sz;
if (nkexec_segments == HOST_KEXEC_SEGMENT_MAX)
panic("Tried to load too many kexec segments");
@ -332,10 +333,22 @@ get_phys_buffer(vm_offset_t dest, const size_t len, void **buf)
goto out;
}
loaded_segments[nkexec_segments].buf = host_getmem(segsize);
loaded_segments[nkexec_segments].bufsz = segsize;
sz = segsize;
if (nkexec_segments == 0) {
/* how much space does this segment have */
sz = space_avail(dest);
/* Clip to 45% of available memory (need 2 copies) */
sz = min(sz, rounddown2(mem_avail * 45 / 100, SEGALIGN));
/* And only use 95% of what we can allocate */
sz = min(sz, rounddown2(
(commit_limit - committed_as) * 95 / 100, SEGALIGN));
printf("Allocating %zd MB for first segment\n", sz >> 20);
}
loaded_segments[nkexec_segments].buf = host_getmem(sz);
loaded_segments[nkexec_segments].bufsz = sz;
loaded_segments[nkexec_segments].mem = (void *)rounddown2(dest,SEGALIGN);
loaded_segments[nkexec_segments].memsz = segsize;
loaded_segments[nkexec_segments].memsz = sz;
i = nkexec_segments;
nkexec_segments++;