linux-kernel - Re: [PATCH] tmpfs: use ida to get inode number

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Message-ID: <20191123045444.GI26530@ZenIV.linux.org.uk>
Date:   Sat, 23 Nov 2019 04:54:44 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     "zhengbin (A)" <zhengbin13@...wei.com>,
        Hugh Dickins <hughd@...gle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, houtao1@...wei.com,
        yi.zhang@...wei.com, "J. R. Okajima" <hooanon05g@...il.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH] tmpfs: use ida to get inode number

On Fri, Nov 22, 2019 at 06:33:25PM -0800, Matthew Wilcox wrote:
> On Sat, Nov 23, 2019 at 10:16:39AM +0800, zhengbin (A) wrote:
> > By the way, percpu IDA is for reducing performance impact? This patch has 2.16%
> > performance degradation(Use perf to get the cost of ida_alloc_range)
> 
> 2.16% degradation in your tests ... I bet Eric didn't make it so complex
> for only 2% performance impact.  Unfortunately, he didn't give any
> numbers in his patch submission, but it's going to be a bigger problem
> on multi-socket machines than on a laptop.

It could also be that socket(2) is called (on real loads) just a bit
more often than open(2) in a benchmark that tests file creation...