Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 05/30/2017 06:06 PM, Andrea Arcangeli wrote:
> 
> I'm not sure if it should be considered a bug, the prctl is intended
> to use normally by wrappers so it looks optimal as implemented this
> way: affecting future vmas only, which will all be created after
> execve executed by the wrapper.
> 
> What's the point of messing with the prctl so it mangles over the
> wrapper process own vmas before exec? Messing with those vmas is pure
> wasted CPUs for the wrapper use case which is what the prctl was
> created for.
> 
> Furthermore there would be the risk a program that uses the prctl not
> as a wrapper and then calls the prctl to clear VM_NOHUGEPAGE from
> def_flags assuming the current kABI. The program could assume those
> vmas that were instantiated before disabling the prctl are still with
> VM_NOHUGEPAGE set (they would not after the change you propose).
> 
> Adding a scan of all vmas to PR_SET_THP_DISABLE to clear VM_NOHUGEPAGE
> on existing vmas looks more complex too and less finegrined so
> probably more complex for userland to manage

I would expect the prctl wouldn't iterate all vma's, nor would it modify
def_flags anymore. It would just set a flag somewhere in mm struct that
would be considered in addition to the per-vma flags when deciding
whether to use THP. We could consider whether MADV_HUGEPAGE should be
able to override the prctl or not.

> but ignoring all above
> considerations it would be a functional alternative for CRIU's
> needs. However if you didn't like the complexity of the new madvise
> which is functionally a one-liner equivalent to MADV_NORMAL, I
> wouldn't expect you to prefer to make the prctl even more complex with
> a loop over all vmas that despite being fairly simple it'll still be
> more than a trivial one liner.
> 
> Thanks,
> Andrea
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@xxxxxxxxx.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
> 

--
To unsubscribe from this list: send the line "unsubscribe linux-api" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html



[Index of Archives]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]

  Powered by Linux