Hello, Andrew. On Thu, Mar 13, 2014 at 02:34:56PM -0700, Andrew Morton wrote: > Jens isn't talking to us. Tejun, are you able explain REQ_SYNC?
It has nothing to do with data integrity. It's just a hint telling the block layer that someone is waiting for the IO so it'd be a good idea to prioritize it. For example, nothing visible to userland really waits for periodic writebacks, so we can delay their processing to prioritize, for example, READs triggered from a page fault, which is obviously causing userland visible latency. Block layer treats all READs as REQ_SYNC and also allows upper layers to mark some writes REQ_SYNC for cases where somebody is waiting for the write to complete for cases like flush(2). > From: Roman Pen <r.peni...@gmail.com> > Subject: fs/mpage.c: forgotten WRITE_SYNC in case of data integrity write > > In case of wbc->sync_mode == WB_SYNC_ALL we need to do data integrity > write, thus mark request as WRITE_SYNC. So, at least this patch description is very misleading. WRITE_SYNC has *NOTHING* to do with data integrity. The only thing matters is whether somebody is waiting for its completion or not. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
