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Date: Thu, 11 Jan 2024 13:54:04 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Jianfeng Wang <jianfeng.w.wang@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>, linux-mm@kvack.org,
 linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm, oom: Add lru_add_drain() in __oom_reap_task_mm()
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On Thu, 11 Jan 2024 10:54:45 -0800 Jianfeng Wang <jianfeng.w.wang@oracle.com> wrote:

> 
> > Unless you can show any actual runtime effect of this patch then I think
> > it shouldn't be merged.
> > 
> 
> Thanks for raising your concern.
> I'd call it a trade-off rather than "not really correct". Look at
> unmap_region() / free_pages_and_swap_cache() written by Linus. These are in
> favor of this pattern, which indicates that the trade-off (i.e. draining
> local CPU or draining all CPUs or no draining at all) had been made in the
> same way in the past. I don't have a specific runtime effect to provide,
> except that it will free 10s kB pages immediately during OOM.

I don't think it's necessary to run lru_add_drain() for each vma.  Once
we've done it it once, it can be skipped for additional vmas.

That's pretty minor because the second and successive calls will be
cheap.  But it becomes much more significant if we switch to
lru_add_drain_all(), which sounds like what we should be doing here. 
Is it possible?