Re: msync() behaviour broken for MS_ASYNC, revert patch?

[Nick Piggin <nickpiggin@yahoo.com.au>]

Andrew Morton wrote:
> Nick Piggin <nickpiggin@yahoo.com.au> wrote:
> 
>>If you want to start the IO *now* without waiting on it, call msync(MS_ASYNC)
>> If you don't want to start the IO now, that's really easy, do nothing.
>> If you want to start the IO now and also wait for it to finish, call msync(MS_SYNC)
> 
> 
> I've already explained the problems with the start-io-in-MS_ASYNC approach.
> 

But I've explained that they only matter for people using it in stupid ways.
fsync also poses a performance problem for programs that call it after every
write(2).

> 
>> Presently, the first option is unavailable.
> 
> 
> We need to patch the kernel either way.  There's no point in going back to
> either the known-problematic approach or to something half-assed.
> 

The system call indicates to the kernel that IO submission should be started.
The earlier the kernel does that, the better (because it is likely that an
MS_SYNC is coming soon).

I think the current way of just moving the dirty bits is half-assed.

Is a more efficient implementation know-problematic? What applications did
you observe problems with, can you remember? Because the current behaviour
is also known-problematic for linux@horizon.com (who are you anyway?)

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SUSE Labs, Novell Inc.
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