From mboxrd@z Thu Jan 1 00:00:00 1970 From: Petr Mladek Date: Thu, 12 Jan 2017 14:18:44 +0000 Subject: Re: [PATCH] mm/page_alloc: Wait for oom_lock before retrying. Message-Id: <20170112141844.GA20462@pathway.suse.cz> List-Id: References: <20161220153948.GA575@tigerII.localdomain> <201612221927.BGE30207.OSFJMFLFOHQtOV@I-love.SAKURA.ne.jp> <20161222134250.GE413@tigerII.localdomain> <201612222301.AFG57832.QOFMSVFOJHLOtF@I-love.SAKURA.ne.jp> <20161222140930.GF413@tigerII.localdomain> <201612261954.FJE69201.OFLVtFJSQFOHMO@I-love.SAKURA.ne.jp> <20161226113407.GA515@tigerII.localdomain> In-Reply-To: <20161226113407.GA515@tigerII.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Sergey Senozhatsky Cc: Tetsuo Handa , mhocko@suse.com, linux-mm@kvack.org, Greg Kroah-Hartman , Jiri Slaby , linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org, sergey.senozhatsky.work@gmail.com On Mon 2016-12-26 20:34:07, Sergey Senozhatsky wrote: > console_trylock() used to always forbid rescheduling; but it got changed > like a yaer ago. > > the other thing is... do we really need to console_conditional_schedule() > from fbcon_*()? console_unlock() does cond_resched() after every line it > prints. wouldn't that be enough? > > so may be we can drop some of console_conditional_schedule() > call sites in fbcon. or update console_conditional_schedule() > function to always return the current preemption value, not the > one we saw in console_trylock(). I was curious if it makes sense to remove console_conditional_schedule() completely. In practice, it never allows rescheduling when the console driver is called via console_unlock(). It is since 2006 and the commit 78944e549d36673eb62 ("vt: printk: Fix framebuffer console triggering might_sleep assertion"). This commit added that console_may_schedule = 0; into console_unlock() before the console drivers are called. On the other hand, it seems that the rescheduling was always enabled when some console operations were called via tty_operations. For example: struct tty_operations con_ops con_ops->con_write() -> do_con_write() #calls console_lock() -> do_con_trol() -> fbcon_scroll() -> fbcon_redraw_move() -> console_conditional_schedule() , where console_lock() sets console_may_schedule = 1; A complete console scroll/redraw might take a while. The rescheduling would make sense => IMHO, we should keep console_conditional_schedule() or some alternative in the console drivers as well. But I am afraid that we could not use the automatic detection. We are not able to detect preemption when CONFIG_PREEMPT_COUNT is disabled. But we still would like to enable rescheduling when called from the tty code (guarded by console_lock()). As a result. We should keep console_may_schedule as a global variable. We cannot put the automatic detection into console_conditional_schedule(). Instead, we need to fix handling of the global variable in console_unlock(). I am going to prepare a patch for this. Best Regards, Petr