linux-kernel - Re: [PATCH] zram_drv: add __GFP_NOMEMALLOC not to use ALLOC_NO

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Date:   Mon, 6 Jun 2022 13:48:12 -0700
From:   Minchan Kim <minchan@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Jaewon Kim <jaewon31.kim@...sung.com>, ngupta@...are.org,
        senozhatsky@...omium.org, avromanov@...rdevices.ru,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        s.suk@...sung.com, ytk.lee@...sung.com, jaewon31.kim@...il.com
Subject: Re: [PATCH] zram_drv: add __GFP_NOMEMALLOC not to use
 ALLOC_NO_WATERMARKS

On Mon, Jun 06, 2022 at 12:59:39PM -0700, Andrew Morton wrote:
> On Mon, 6 Jun 2022 12:46:38 -0700 Minchan Kim <minchan@...nel.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?

For me, I usually tries to remove GFP_ATOMIC alllocation since the
atomic allocation can be failed easily(zram is not only source for
it). Otherwise, increase min_free_kbytes?