On (13/12/07 14:29), Andrew Morton didst pronounce:
> > The simple way seems to be to malloc a large area, touch every page and
> > then look at the physical pages assigned ... they now mostly seem to be
> > descending in physical address.
> >
>
> OIC. -mm's /proc/pid/pagemap can be used to get the pfn's...
>
I tried using pagemap to verify the patch but it triggered BUG_ON
checks. Perhaps I am using the interface wrong but I would still not
expect it to break in this fashion. I tried 2.6.24-rc4-mm1, 2.6.24-rc5-mm1,
2.6.24-rc5 with just the maps4 patches applied and 2.6.23 with maps4 patches
applied. Each time I get errors like this;
[ 90.108315] BUG: sleeping function called from invalid context at
include/asm/uaccess_32.h:457
[ 90.211227] in_atomic():1, irqs_disabled():0
[ 90.262251] no locks held by showcontiguous/2814.
[ 90.318475] Pid: 2814, comm: showcontiguous Not tainted 2.6.24-rc5 #1
[ 90.395344] [<c010522a>] show_trace_log_lvl+0x1a/0x30
[ 90.456948] [<c0105bb2>] show_trace+0x12/0x20
[ 90.510173] [<c0105eee>] dump_stack+0x6e/0x80
[ 90.563409] [<c01205b3>] __might_sleep+0xc3/0xe0
[ 90.619765] [<c02264fd>] copy_to_user+0x3d/0x60
[ 90.675153] [<c01b3e9c>] add_to_pagemap+0x5c/0x80
[ 90.732513] [<c01b43e8>] pagemap_pte_range+0x68/0xb0
[ 90.793010] [<c0175ed2>] walk_page_range+0x112/0x210
[ 90.853482] [<c01b47c6>] pagemap_read+0x176/0x220
[ 90.910863] [<c0182dc4>] vfs_read+0x94/0x150
[ 90.963058] [<c01832fd>] sys_read+0x3d/0x70
[ 91.014219] [<c0104262>] syscall_call+0x7/0xb
[ 91.067433] =======================
[ 91.110137] BUG: scheduling while atomic: showcontiguous/2814/0x00000001
[ 91.190169] no locks held by showcontiguous/2814.
[ 91.246293] Pid: 2814, comm: showcontiguous Not tainted 2.6.24-rc5 #1
[ 91.323145] [<c010522a>] show_trace_log_lvl+0x1a/0x30
[ 91.384633] [<c0105bb2>] show_trace+0x12/0x20
[ 91.437878] [<c0105eee>] dump_stack+0x6e/0x80
[ 91.491116] [<c0123816>] __schedule_bug+0x66/0x70
[ 91.548467] [<c033ba96>] schedule+0x556/0x7b0
[ 91.601698] [<c01042e6>] work_resched+0x5/0x21
[ 91.655977] =======================
[ 91.704927] showcontiguous[2814]: segfault at b7eaa900 eip b7eaa900 esp
bfa02e8c error 4
[ 91.801633] BUG: scheduling while atomic: showcontiguous/2814/0x00000001
[ 91.881634] no locks held by showcontiguous/2814.
[ 91.937779] Pid: 2814, comm: showcontiguous Not tainted 2.6.24-rc5 #1
[ 92.014606] [<c010522a>] show_trace_log_lvl+0x1a/0x30
[ 92.076123] [<c0105bb2>] show_trace+0x12/0x20
[ 92.129354] [<c0105eee>] dump_stack+0x6e/0x80
[ 92.182567] [<c0123816>] __schedule_bug+0x66/0x70
[ 92.239959] [<c033ba96>] schedule+0x556/0x7b0
[ 92.293187] [<c01042e6>] work_resched+0x5/0x21
[ 92.347452] =======================
[ 92.392697] note: showcontiguous[2814] exited with preempt_count 1
[ 92.468611] BUG: scheduling while atomic: showcontiguous/2814/0x10000001
[ 92.548588] no locks held by showcontiguous/2814.
[ 92.604732] Pid: 2814, comm: showcontiguous Not tainted 2.6.24-rc5 #1
[ 92.681665] [<c010522a>] show_trace_log_lvl+0x1a/0x30
[ 92.743180] [<c0105bb2>] show_trace+0x12/0x20
[ 92.796409] [<c0105eee>] dump_stack+0x6e/0x80
[ 92.849621] [<c0123816>] __schedule_bug+0x66/0x70
[ 92.907014] [<c033ba96>] schedule+0x556/0x7b0
[ 92.960349] [<c0123847>] __cond_resched+0x27/0x40
[ 93.017804] [<c033be3a>] cond_resched+0x2a/0x40
[ 93.073122] [<c016e22c>] unmap_vmas+0x4ec/0x540
[ 93.128418] [<c017132f>] exit_mmap+0x6f/0xf0
[ 93.180611] [<c01254d1>] mmput+0x31/0xb0
[ 93.228665] [<c01295fd>] exit_mm+0x8d/0xf0
[ 93.278788] [<c012ac8f>] do_exit+0x15f/0x7e0
[ 93.330965] [<c012b339>] do_group_exit+0x29/0x70
[ 93.387321] [<c0133e07>] get_signal_to_deliver+0x2b7/0x490
[ 93.454013] [<c010373d>] do_notify_resume+0x7d/0x760
[ 93.514476] [<c0104315>] work_notifysig+0x13/0x1a
[ 93.571869] =======================
Just using cp to read the file is enough to cause problems but I included
a very basic program below that produces the BUG_ON checks. Is this a known
issue or am I using the interface incorrectly?
#include <stdio.h>
#include <sys/mman.h>
#include <stdlib.h>
#include <unistd.h>
#include <linux/types.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#define MAPSIZE (4*1048576)
#define PM_ENTRY_BYTES sizeof(__u64)
int main(int argc, char **argv)
{
int pagemap_fd;
unsigned long *anonmapping;
__u64 pagemap_entry = 0ULL;
unsigned long vpfn, ppfn;
size_t mmap_offset;
int pagesize = getpagesize();
/* Open the pagemap interface */
pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
if (pagemap_fd == -1) {
perror("fopen");
exit(EXIT_FAILURE);
}
/* Create an anonymous mapping */
anonmapping = mmap(NULL, MAPSIZE,
PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS|MAP_POPULATE,
-1, 0);
if (anonmapping == MAP_FAILED) {
perror("mmap");
exit(1);
}
/* Work out the VPN the mapping is at and seek to it in pagemap */
vpfn = ((unsigned long)anonmapping) / pagesize;
mmap_offset = lseek(pagemap_fd, vpfn * PM_ENTRY_BYTES, SEEK_SET);
if (mmap_offset == -1) {
perror("fseek");
exit(EXIT_FAILURE);
}
/* Read the PFN of each page in the mapping */
for (mmap_offset = 0; mmap_offset < MAPSIZE; mmap_offset += pagesize) {
vpfn = ((unsigned long)anonmapping + mmap_offset) / pagesize;
if (read(pagemap_fd, &pagemap_entry, PM_ENTRY_BYTES) == 0) {
perror("fread");
exit(EXIT_FAILURE);
}
ppfn = (unsigned long)pagemap_entry;
printf("vpfn = %8lu ppfn = %8lu\n", vpfn, ppfn);
}
close(pagemap_fd);
munmap(anonmapping, MAPSIZE);
exit(EXIT_SUCCESS);
}
--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
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