Re: [PATCH] zram_drv: add __GFP_NOMEMALLOC not to use ALLOC_NO_WATERMARKS

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 6 Jun 2022 12:46:38 -0700 Minchan Kim <minchan@kernel.org> wrote:

> On Fri, Jun 03, 2022 at 02:57:47PM +0900, Jaewon Kim wrote:
> > The atomic page allocation failure sometimes happened, and most of them
> > seem to occur during boot time.
> > 
> > <4>[   59.707645] system_server: page allocation failure: order:0, mode:0xa20(GFP_ATOMIC), nodemask=(null),cpuset=foreground-boost,mems_allowed=0
>
> ...
>
> > 
> > The kswapd or other reclaim contexts may not prepare enough free pages
> > for too many atomic allocations occurred in short time. But zram may not
> > be helpful for this atomic allocation even though zram is used to
> > reclaim.
> > 
> > To get one zs object for a specific size, zram may allocate serveral
> > pages. And this can be happened on different class sizes at the same
> > time. It means zram may consume more pages to reclaim only one page.
> > This inefficiency may consume all free pages below watmerk min by a
> > process having PF_MEMALLOC like kswapd.
> 
> However, that's how zram has worked for a long time(allocate memory
> under memory pressure) and many folks already have raised min_free_kbytes
> when they use zram as swap. If we don't allow the allocation, swap out
> fails easier than old, which would break existing tunes.

So is there a better way of preventing this warning?  Just suppress it
with __GFP_NOWARN?