Messages in this thread | | | Date | Sun, 30 Jan 2011 02:26:27 -0800 | Subject | Re: [PATCH] mlock: revert the optimization for dirtying pages and triggering writeback. | From | Michel Lespinasse <> |
| |
On Sat, Jan 29, 2011 at 11:15 PM, Tao Ma <tm@tao.ma> wrote: > buf = mmap(NULL, file_len, PROT_WRITE, MAP_SHARED, fd, 0); > if (buf == MAP_FAILED) { > perror("mmap"); > goto out; > } > > if (mlock(buf, file_len) < 0) { > perror("mlock"); > goto out; > }
Thanks Tao for tracing this to an individual change. I can reproduce this on my system. The issue is that the file is mapped without the PROT_READ permission, so mlock can't fault in the pages. Up to 2.6.37 this worked because mlock was using a write.
The test case does show there was a behavior change; however it's not clear to me that the tested behavior is valid.
I can see two possible resolutions:
1- do nothing, if we can agree that the test case is invalid
2- restore the previous behavior for writable, non-readable, shared mappings while preserving the optimization for read/write shared mappings. The test would then look like: if ((vma->vm_flags & VM_WRITE) && (vma->vm_flags & (VM_READ | VM_SHARED)) != VM_SHARED) gup_flags |= FOLL_WRITE;
-- Michel "Walken" Lespinasse A program is never fully debugged until the last user dies. -- 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/
| |