Kernel: purge() incorrectly clears dirty pages
When clearing pages purge() drops dirty pages for inode VM objects because we're not tracking whether a page was dirtied. This can be observed by calling purge -c when the following test program is running:
#include <LibMain/Main.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <unistd.h>
ErrorOr<int> serenity_main(Main::Arguments)
{
int fd = open("/etc/fstab", O_RDONLY);
char* p = (char*)mmap(nullptr, 4096, PROT_READ | PROT_WRITE, MAP_FILE | MAP_PRIVATE, fd, 0);
close(fd);
uintptr_t zero { 0 };
memcpy(p, &zero, sizeof(zero));
for (;;) {
sleep(1);
VERIFY(memcmp(p, &zero, sizeof(zero)) == 0);
}
return 0;
}
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