linux-kernel - Re: [PATCH] mm/page_alloc: Wait for oom

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Date:   Fri, 13 Jan 2017 13:15:36 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        mhocko@...e.com, linux-mm@...ck.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.cz>, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/page_alloc: Wait for oom_lock before retrying.

On Fri 2017-01-13 20:50:24, Sergey Senozhatsky wrote:
> On (01/13/17 12:03), Petr Mladek wrote:
> [..]
> > > why can't we?
> > 
> > Because it would newer call cond_resched() in non-preemptive kernel
> > with CONFIG_PREEMPT_COUNT disabled. IMHO, we want to call it,
> > for example, when we scroll the entire screen from tty_operations.
> > 
> > Or do I miss anything?
> 
> so... basically. it has never called cond_resched() there. right?
> why is this suddenly a problem now?

But it called cond_resched() when the very same code was called
from tty operations under console_lock() that forced
console_may_schedule = 1;

It will never call cond_resched() from the tty operations
when CONFIG_PREEMPT_COUNT is disabled and we try to detect
the preemption automatically.

Best Regards,
Petr