Messages in this thread | | | Date | Thu, 17 Aug 2006 22:34:46 -0700 | From | Andrew Morton <> | Subject | Re: RFC - how to balance Dirty+Writeback in the face of slow writeback. |
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On Thu, 17 Aug 2006 12:18:52 -0400 Trond Myklebust <trond.myklebust@fys.uio.no> wrote:
> On Thu, 2006-08-17 at 08:30 -0700, Andrew Morton wrote: > > On Thu, 17 Aug 2006 09:21:51 -0400 > > Trond Myklebust <trond.myklebust@fys.uio.no> wrote: > > > Exactly how would a request limit help? All that boils down to is having > > > the VM monitor global_page_state(NR_FILE_DIRTY) versus monitoring > > > global_page_state(NR_FILE_DIRTY)+global_page_state(NR_WRITEBACK). > > > > > > > I assume that if NFS is not limiting its NR_WRITEBACK consumption and block > > devices are doing so, we could get in a situation where NFS hogs all of the > > fixed-size NR_DIRTY+NR_WRITEBACK resource at the expense of concurrent > > block-device-based writeback. > > Since NFS has no control over NR_DIRTY, how does controlling > NR_WRITEBACK help? The only resource that NFS shares with the block > device writeout queues is memory.
Block devices have a limit on the amount of IO which they will queue. NFS doesn't.
> IOW: The resource that needs to be controlled is the dirty pages, not > the write-out queue. Unless you can throttle back on the creation of > dirty NFS pages in the first place, then the potential for unfairness > will exist.
Please read the whole thread - we're violently agreeing. - 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/
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