Re: [PATCH v2 0/6] tmpfs: add the option to disable swap

[Luis Chamberlain <mcgrof@kernel.org>]

On Mon, Mar 20, 2023 at 07:14:22PM +0800, haoxin wrote:
> 
> 在 2023/3/20 上午4:32, Luis Chamberlain 写道:
> > On Tue, Mar 14, 2023 at 10:46:28AM +0800, haoxin wrote:
> > > All these series looks good to me and i do some test on my virtual machine
> > > it works well.
> > > 
> > > so please add Tested-by: Xin Hao<xhao@linux.alibaba.com>  .
> > > 
> > > just one question, if tmpfs pagecache occupies a large amount of memory, how
> > > can we ensure successful memory reclamation in case of memory shortage?
> > If you're disabling swap then you know the only thing you can do is
> > unmount if you want to help the VM, otherwise the pressure is just
> > greater for the VM.
> 
> Un, what i mean is can we add a priority so that this type of pagecache is
> reclaimed last ?

That seems to be a classifier request for something much less aggressive
than mapping_set_unevictable(). My patches *prior* to using mapping_set_unevictable()
are I think closer to what it seems you want, but as noted before by
folks, that also puts unecessary stress on the VM because just fail
reclaim on our writepage().

> Instead of just setting the parameter noswap to make it unreclaimed, because
> if such pagecache which occupy big part of memory which can not be
> reclaimed, it will cause OOM.

You can't simultaneously retain possession of a cake and eat it, too,
once you eat it, its gone and noswap eats the cake because of the
suggestion / decision to follow through with mapping_set_unevictable().

It sounds like you want to make mapping_set_unevictable() optional and
deal with the possible stress incurred writepage() failing? Not quite
sure what else to recommend here.

  Luis