linux-kernel - Re: [RFC PATCH 0/5] kmalloc-reclaimable caches

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Message-ID: <20180524114350.GA10323@bombadil.infradead.org>
Date:   Thu, 24 May 2018 04:43:50 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     linux-mm@...ck.org, Roman Gushchin <guro@...com>,
        Michal Hocko <mhocko@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Vijayanand Jitta <vjitta@...eaurora.org>
Subject: Re: [RFC PATCH 0/5] kmalloc-reclaimable caches

On Thu, May 24, 2018 at 01:00:06PM +0200, Vlastimil Babka wrote:
> Now for the issues a.k.a. why RFC:
> 
> - I haven't find any other obvious users for reclaimable kmalloc (yet)

Is that a problem?  This sounds like it's enough to solve Facebook's
problem.

> - the name of caches kmalloc-reclaimable-X is rather long

Yes; Christoph and I were talking about restricting slab names to 16 bytes
just to make /proc/slabinfo easier to read.  How about

kmalloc-rec-128k
1234567890123456

Just makes it ;-)

Of course, somebody needs to do the work to use k/M instead of 4194304.
We also need to bikeshed about when to switch; should it be:

kmalloc-rec-512
kmalloc-rec-1024
kmalloc-rec-2048
kmalloc-rec-4096
kmalloc-rec-8192
kmalloc-rec-16k

or should it be

kmalloc-rec-512
kmalloc-rec-1k
kmalloc-rec-2k
kmalloc-rec-4k
kmalloc-rec-8k
kmalloc-rec-16k

I slightly favour the latter as it'll be easier to implement.  Something like

	static const char suffixes[3] = ' kM';
	int idx = 0;

	while (size > 1024) {
		size /= 1024;
		idx++;
	}

	sprintf("%d%c", size, suffices[idx]);