Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964829AbWL1AkN (ORCPT ); Wed, 27 Dec 2006 19:40:13 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S964827AbWL1AkN (ORCPT ); Wed, 27 Dec 2006 19:40:13 -0500 Received: from smtp.osdl.org ([65.172.181.25]:46577 "EHLO smtp.osdl.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964829AbWL1AkL (ORCPT ); Wed, 27 Dec 2006 19:40:11 -0500 Date: Wed, 27 Dec 2006 16:39:43 -0800 (PST) From: Linus Torvalds To: David Miller cc: ranma@tdiedrich.de, gordonfarquharson@gmail.com, tbm@cyrius.com, a.p.zijlstra@chello.nl, andrei.popa@i-neo.ro, Andrew Morton , hugh@veritas.com, nickpiggin@yahoo.com.au, arjan@infradead.org, Linux Kernel Mailing List Subject: Re: [PATCH] mm: fix page_mkclean_one In-Reply-To: Message-ID: References: <97a0a9ac0612240010x33f4c51cj32d89cb5b08d4332@mail.gmail.com> <20061226161700.GA14128@yamamaya.is-a-geek.org> <20061226.205518.63739038.davem@davemloft.net> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2942 Lines: 118 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 #include #include #include #include #include #include #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/