Re: [RFC][PATCH 4/5] memory_pressure_notify() caller

["Daniel Spång" <daniel.spang@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 2560 bytes --]

On 1/16/08, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:
> Hi Daniel
>
> > > > The notification fires after only ~100 MB allocated, i.e., when page
> > > > reclaim is beginning to nag from page cache. Isn't this a bit early?
> > > > Repeating the test with swap enabled results in a notification after
> > > > ~600 MB allocated, which is more reasonable and just before the system
> > > > starts to swap.
> > >
> > > Your issue may have more to do with the fact that the
> > > highmem zone is 128MB in size and some balancing issues
> > > between __alloc_pages and try_to_free_pages.
> >
> > I don't think so. I ran the test again without highmem and noticed the
> > same behaviour:
>
> Thank you for good point out!
> Could you please post your test program and reproduced method?

Sure:

1. Fill almost all available memory with page cache in a system without swap.
2. Run attached alloc-test program.
3. Notification fires when page cache is reclaimed.

Example:

$ cat /bigfile > /dev/null
$ cat /proc/meminfo
MemTotal:       895876 kB
MemFree:         94272 kB
Buffers:           884 kB
Cached:         782868 kB
SwapCached:          0 kB
Active:          15356 kB
Inactive:       778000 kB
HighTotal:           0 kB
HighFree:            0 kB
LowTotal:       895876 kB
LowFree:         94272 kB
SwapTotal:           0 kB
SwapFree:            0 kB
Dirty:               0 kB
Writeback:           0 kB
AnonPages:        9624 kB
Mapped:           1352 kB
Slab:             4220 kB
SReclaimable:     1168 kB
SUnreclaim:       3052 kB
PageTables:        528 kB
NFS_Unstable:        0 kB
Bounce:              0 kB
CommitLimit:    447936 kB
Committed_AS:    28988 kB
VmallocTotal:   122872 kB
VmallocUsed:       904 kB
VmallocChunk:   121864 kB
$ ./test-alloc
---------
Got notification, allocated 90 MB
$ cat /proc/meminfo
MemTotal:       895876 kB
MemFree:        101960 kB
Buffers:           888 kB
Cached:         775200 kB
SwapCached:          0 kB
Active:          15356 kB
Inactive:       770336 kB
HighTotal:           0 kB
HighFree:            0 kB
LowTotal:       895876 kB
LowFree:        101960 kB
SwapTotal:           0 kB
SwapFree:            0 kB
Dirty:              28 kB
Writeback:           0 kB
AnonPages:        9624 kB
Mapped:           1352 kB
Slab:             4224 kB
SReclaimable:     1168 kB
SUnreclaim:       3056 kB
PageTables:        532 kB
NFS_Unstable:        0 kB
Bounce:              0 kB
CommitLimit:    447936 kB
Committed_AS:    28988 kB
VmallocTotal:   122872 kB
VmallocUsed:       904 kB
VmallocChunk:   121864 kB

[-- Attachment #2: alloc-test.c --]
[-- Type: application/octet-stream, Size: 1738 bytes --]

/*
 * Allocate 10 MB each second. Exit on notification.
 */

#include <sys/mman.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <poll.h>
#include <pthread.h>
#include <errno.h>

int count = 0;
int size = 10;

void *do_alloc() 
{
        for(;;) {
                int *buffer;
                buffer = mmap(NULL,  size*1024*1024,
                              PROT_READ | PROT_WRITE,
                              MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
                if (buffer == MAP_FAILED) {
                        perror("mmap");
                        exit(EXIT_FAILURE);
                }
                memset(buffer, 1 , size*1024*1024);

                printf("-");
                fflush(stdout);

                count++;
                sleep(1);
        }
}

int wait_for_notification(struct pollfd *pfd)
{
        int ret;
        read(pfd->fd, 0, 0);
        ret = poll(pfd, 1, -1);
        if (ret == -1 && errno != EINTR) {
                perror("poll");
                exit(EXIT_FAILURE);
        }
        return ret;
}

void do_free() 
{
        struct pollfd pfd;

        pfd.fd = open("/dev/mem_notify", O_RDONLY);
        if (pfd.fd == -1) {
                perror("open");
                exit(EXIT_FAILURE);
        }
        pfd.events = POLLIN;
        for(;;)
                if (wait_for_notification(&pfd) > 0) {
                        printf("\nGot notification, allocated %d MB\n",
                               size * count);
                        exit(EXIT_SUCCESS);
                }
}

int main(int argc, char *argv[])
{
        pthread_t allocator;

        pthread_create(&allocator, NULL, do_alloc, NULL);
        do_free();
}