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kalloc: never-used memory stays a range; 256 GB; free is a counter

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Every page of RAM went onto the free list at boot, which means writing
each one -- a link, and kfree()'s 4 KB of junk -- before the first
process ran: 64 GB of memset on a 64 GB machine to say it was free.
Memory nobody has used yet is kept as a cursor and an end per region
now, and kalloc() takes from those once the list of given-back pages
is empty. A page is first touched by whoever asked for it.

That makes the cap on RAM cheap to raise, and PHYSTOP_MAX goes from 64
to 256 GB, which still leaves 248 GB of the kernel PDPT for device
windows. MEMREGION_MAX goes from 32 to 64 for the firmware maps that
cut RAM into many pieces.

kalloc_free_bytes() walked the whole free list under the allocator's
lock -- two million links on 8 GB, every second top or fastfetch was
running, with every CPU that wanted a page waiting behind it. It reads
a counter now. And the buffer cache, which keeps what it grows to, is
reported as Buffers in /proc/meminfo and sysinfo(2) rather than as
memory used by nothing.

Checked under QEMU at 1, 2 and 6 GB: MemFree right, zsh splitting
200000 words, fork loops, a 74 MB write.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
This commit is contained in:
Nexoniarz 2026-10-23 14:05:40 +02:00
commit b70e36e0a2
4 changed files with 106 additions and 23 deletions
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8
kernel/sys/sys_proc.c
View file

@ -12,6 +12,10 @@
#include "errno.h"
#include "acpi.h"
#include "fat.h"
#include "spinlock.h"
#include "sleeplock.h"
#include "fs.h"
#include "buf.h"
addr_t sys_fork(void) { return fork(); }
addr_t sys_wait(void) { return wait(); }
@ -522,6 +526,10 @@ addr_t sys_sysinfo(void)
// then PHYSTOP, an address, which counted the PCI hole as memory.
si->totalram = ram_total_bytes();
si->freeram = kalloc_free_bytes();
// The buffer cache, so free(1) does not count it as used by nothing.
uint nbuf, maxbuf;
bcache_size(&nbuf, &maxbuf);
si->bufferram = (uint64)nbuf * BSIZE;
si->mem_unit = 1;
si->procs = (uint16)proc_num();
return 0;