On Mon, Apr 21, 2014 at 11:14:31AM -0700, Christoph Hellwig wrote: > > 6. On Linux, MS_ASYNC is also a no-op. That's fine on a unified > > cache system. Filesystem I/O always sees a consistent view, > > and MS_ASYNC never undertook to give a guarantee about *when* > > the update would occur. (The Linux buffer cache logic will > > ensure that it is flushed out sometime in the near future.) > > Right. It's a fairly inefficient noop, though - it actually loops > over all vmas to do nothing with them. This will probably change for Persistent Memory. The reason it works today is that we have a page cache which tracks dirty bits and periodically writes dirty pages to storage. If we bypass the page cache, we have to ensure that everything does still eventually get synced. I don't quite know how this is going to work yet ... I have a number of ideas in my head. It probably won't be asynchronous though! > > 7. On Linux (and probably many other modern systems), the only > > call that has any real use is msync(MS_SYNC), meaning > > "flush the buffers *now*, and I want to wait for that to > > complete, so that I can then continue safe in the knowledge > > that my data has landed on a device". That's useful if we > > want insurance for our data in the event of a system crash. > > Right. It's basically another way to call fsync, which is used to > implement it underneath. It actually should be a ranged-fdatasync > but right it's it's implemented horribly inefficiently in that it > does a fsync call for each vma that it encounters in the range > specified. See also: From: Matthew Wilcox <matthew.r.wilcox@xxxxxxxxx> To: linux-mm@xxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx Cc: Matthew Wilcox <matthew.r.wilcox@xxxxxxxxx>, willy@xxxxxxxxxxxxxxx Subject: [PATCH] Sync only the requested range in msync Date: Thu, 27 Mar 2014 19:02:41 -0400 Message-Id: <1395961361-21307-1-git-send-email-matthew.r.wilcox@xxxxxxxxx> -- 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
