On 2012-12-11 21:10, Ken Raeburn wrote: > On 12/11/12 08:29, Jens Axboe wrote: >> You are right, blkid likely wont be done by then, so it's still down >> to timing whether it'll help or not. This is pretty annoying. This >> issue is due to the file being opened for write. But unfortunately we >> cannot open for read always, as fcntl() wont allow change of file >> access mode flags. So how about the below. Basically DON'T close the >> fd, defer that until we really close the file. This will keep one >> extra fd open until the original is closed, but I don't see that as >> being an issue. > > This patch seems to be working just fine. I have reproduced the case > where it uses the shadow_fd field, but blkid doesn't run and the page > cache entries don't get loaded, and in my initial tests with dm-zero, it > looks like the bimodal performance distribution is gone. > > Thanks! Excellent, I think this is probably as good as it is going to get. I have committed the fix. Thanks a lot for reporting it, especially in such great detail. When a problem is fully understood, fixing it is then the smallest part of the effort. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe fio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
