Date: Mon, 5 Jul 2021 22:31:26 +0300 From: Vitaliy Gusev <gusev.vitaliy@gmail.com> To: Konstantin Belousov <kostikbel@gmail.com> Cc: freebsd-hackers@freebsd.org, Mark Johnston <markj@freebsd.org> Subject: Re: madvise(MADV_FREE) doesn't work in some cases? Message-ID: <59F26FB5-3A88-42C5-816F-B877977CBA6B@gmail.com> In-Reply-To: <57BCE463-6200-4F83-A321-2F0444E7F063@gmail.com> References: <0A95973D-254A-4574-8DC7-9F515F60B873@gmail.com> <YOBLn/XHpmEBfAdw@kib.kiev.ua> <57BCE463-6200-4F83-A321-2F0444E7F063@gmail.com>
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Further investigation shown that if use MADV_DONTNEED in simple mmap =
test program and run it twice (second after the first finishes =
madvise()), then memory is not freed at all and first instance is =
killed.
If change MADV_DONTNEED flag with MADV_FREE, then memory is freed.
Code is:
#include <sys/mman.h>
#include <err.h>
#include <stdint.h>
#include <sys/cdefs.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
int main(int argc, char *argv[])
{
size_t len =3D (size_t)(argc > 1 ? atoi(argv[1]) : 1024) * 1024 =
* 1024;
uint8_t *ptr, *end;
uint8_t *p;
int pagesz =3D (1<<12);
ptr =3D (uint8_t *)mmap(NULL, len, PROT_WRITE | PROT_READ, =
MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
if (ptr =3D=3D MAP_FAILED)
err(1, "cannot mmap");
end =3D ptr + len;
p =3D ptr;
while (p < end) {
*(uint64_t *)p =3D 1;
p +=3D pagesz;
}
sleep(1);
printf("madvise\n");
p =3D ptr;
while (p < end) {
int error;
error =3D madvise(p, pagesz, MADV_DONTNEED);
if (error) {
err(1, "cannot madvise");
}
p +=3D pagesz;
}
printf("press Enter to exit\n");
getchar();
}
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