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From:   Uladzislau Rezki <urezki@gmail.com>
Date:   Wed, 30 Sep 2020 14:31:53 +0200
To:     Michal Hocko <mhocko@suse.com>,
        "Paul E. McKenney" <paulmck@kernel.org>
Cc:     "Paul E. McKenney" <paulmck@kernel.org>, rcu@vger.kernel.org,
        linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org,
        jiangshanlai@gmail.com, akpm@linux-foundation.org,
        mathieu.desnoyers@efficios.com, josh@joshtriplett.org,
        tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org,
        dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com,
        oleg@redhat.com, joel@joelfernandes.org,
        mgorman@techsingularity.net, torvalds@linux-foundation.org,
        "Uladzislau Rezki (Sony)" <urezki@gmail.com>
Subject: Re: [PATCH tip/core/rcu 14/15] rcu/tree: Allocate a page when caller
 is preemptible
Message-ID: <20200930123153.GA18005@pc636>
References: <20200928233041.GA23230@paulmck-ThinkPad-P72>
 <20200928233102.24265-14-paulmck@kernel.org>
 <20200929120756.GC2277@dhcp22.suse.cz>
 <20200930015327.GX29330@paulmck-ThinkPad-P72>
 <20200930084139.GN2277@dhcp22.suse.cz>
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>
> > > What is the point of calling kmalloc  for a PAGE_SIZE object? Wouldn't
> > > using the page allocator directly be better?
> > 
> > Well, you guys gave me considerable heat about abusing internal allocator
> > interfaces, and kmalloc() and kfree() seem to be about as non-internal
> > as you can get and still be invoking the allocator.  ;-)
> 
> alloc_pages resp. __get_free_pages is a normal page allocator interface
> to use for page size granular allocations. kmalloc is for more fine
> grained allocations.
>
I do not have a strong opinion here but i would tend to using of the page
allocator directly. Because we operate on a page level where the page
allocator is supposed to be used. From the other hand i saw a slightly
better performance in case of SLAB only. I think that is because of
a) slab caches; b) more objects which can be cached. But i have one more
concern about using of kmalloc(). That is about fragmentations it can
cause with PAGE_SIZE requests.

As for SLUB it was identical whereas the SLOB i din not check.

--
Vlad Rezki