Messages in this thread | | | Date | Wed, 27 Dec 2006 16:39:43 -0800 (PST) | From | Linus Torvalds <> | Subject | Re: [PATCH] mm: fix page_mkclean_one |
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On Wed, 27 Dec 2006, Linus Torvalds wrote: > > I think the test-case could probably be improved by having a munmap() and > page-cache flush in between the writing and the checking, to see whether > that shows the corruption easier (and possibly without having to start > paging in order to throw the pages out, which would simplify testing a > lot).
I think the page-writeout is implicated, because I do seem to need it, but the page-cache flush does seem to make corruption _easier_ to see. I now seem about to trigger it with a 100MB file on a 256MB machine in a minute or so, with this slight modification.
I still don't see _why_, though. But maybe smarter people than me can see it..
Linus
--- #include <sys/mman.h> #include <sys/fcntl.h> #include <unistd.h> #include <stdlib.h> #include <string.h> #include <stdio.h> #include <time.h>
#define TARGETSIZE (100 << 20) #define CHUNKSIZE (1460) #define NRCHUNKS (TARGETSIZE / CHUNKSIZE) #define SIZE (NRCHUNKS * CHUNKSIZE)
static void fillmem(void *start, int nr) { memset(start, nr, CHUNKSIZE); }
static void checkmem(void *start, int nr) { unsigned char c = nr, *p = start; int i; for (i = 0; i < CHUNKSIZE; i++) { if (*p++ != c) { printf("Chunk %d corrupted \n", nr); return; } } }
static char *remap(int fd, char *mapping) { if (mapping) { munmap(mapping, SIZE); posix_fadvise(fd, 0, SIZE, POSIX_FADV_DONTNEED); } return mmap(NULL, SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); }
int main(int argc, char **argv) { char *mapping; int fd, i; static int chunkorder[NRCHUNKS];
/* * Make some random ordering of writing the chunks to the * memory map.. * * Start with fully ordered.. */ for (i = 0; i < NRCHUNKS; i++) chunkorder[i] = i;
/* ..and then mix it up randomly */ srandom(time(NULL)); for (i = 0; i < NRCHUNKS; i++) { int index = (unsigned int) random() % NRCHUNKS; int nr = chunkorder[index]; chunkorder[index] = chunkorder[i]; chunkorder[i] = nr; }
fd = open("mapfile", O_RDWR | O_TRUNC | O_CREAT, 0666); if (fd < 0) return -1; if (ftruncate(fd, SIZE) < 0) return -1; mapping = remap(fd, NULL); if (-1 == (int)(long)mapping) return -1;
for (i = 0; i < NRCHUNKS; i++) { int chunk = chunkorder[i]; printf("Writing chunk %d/%d (%d%%) \r", i, NRCHUNKS, 100*i/NRCHUNKS); fillmem(mapping + chunk * CHUNKSIZE, chunk); } printf("\n");
/* Unmap, drop, and remap.. */ mapping = remap(fd, mapping);
/* .. and check */ for (i = 0; i < NRCHUNKS; i++) { int chunk = i; printf("Checking chunk %d/%d (%d%%) \r", i, NRCHUNKS, 100*i/NRCHUNKS); checkmem(mapping + chunk * CHUNKSIZE, chunk); } printf("\n"); return 0; } - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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