On 04/20/2012 10:52 AM, Zach Brown wrote: > On 04/20/2012 11:20 AM, Jeff Moyer wrote: >> Dave Kleikamp<dave.kleikamp@xxxxxxxxxx> writes: >> >>> On 04/20/2012 09:48 AM, Maxim V. Patlasov wrote: >>>> On 03/30/2012 07:43 PM, Dave Kleikamp wrote: >>>>> From: Zach Brown<zab@xxxxxxxxx> >>>>> >>>>> This uses the new kernel aio interface to process loopback IO by >>>>> submitting concurrent direct aio. Previously loop's IO was serialized >>>>> by synchronous processing in a thread. >>>>> >>>> >>>> The patch ignores REQ_FLUSH bit of bi_rw. Is it simply overlook? >>> >>> Good question. Since the loop device is sending only direct IO requests, >>> it shouldn't be necessary to explicitly flush page cache, but REQ_FLUSH >> >> REQ_FLUSH isn't about the page cache, it's about flushing the volatile >> disk write cache. You need to handle that. > > I guess O_DIRECT doesn't routinely issue flushes simply because it's too > expensive? Apps that care about consistent IO and O_DIRECT are expected > to not have writeback caching enabled? 'cause there's no way they're > issuing syncs themselves. If we weren't using aio, we might be okay, but we don't know that any prior asynchronous request has completed. > > So yeah, I'd agree that the loop code should be reworked a bit so that > both the filebacked and aio methods call vfs_sync() when they see > REQ_FLUSH. It's an easy fix. I don't anticipate that it will hurt performance too badly. > > Bleh. > > - z > (Sorry, no real time to dig into this now. Lots more time in two months!) -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
