linux-kernel - Re: [RFC-PATCH 1/2] mm: Add __GFP_NO

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Message-ID: <20200818154502.GA32169@pc636>
Date:   Tue, 18 Aug 2020 17:45:02 +0200
From:   Uladzislau Rezki <urezki@...il.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, RCU <rcu@...r.kernel.org>,
        linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Matthew Wilcox <willy@...radead.org>,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Joel Fernandes <joel@...lfernandes.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>
Subject: Re: [RFC-PATCH 1/2] mm: Add __GFP_NO_LOCKS flag

Hello, Michal.

You mentioned somewhere in the thread to show figures regarding hitting
a fast path and "fallback one". We follow fallback when a page allocation fails.

Please see below the plot. I hope it is easy to understand:

wget ftp://vps418301.ovh.net/incoming/1000000_kfree_rcu_fast_hit_vs_fallback_hit.png

to summarize. When i tight loop is applied, i.e. flood simulation the fallback hit
is negligible. It is a noise, out of 1 000 000 we have 1% or %2 of fallback hitting.

Thanks!

--
Vlad Rezki