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From: Shakeel Butt <shakeelb@google.com>
To: Daniel Xu <dxu@dxuuu.xyz>
Cc: bpf <bpf@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Linux MM <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Kernel Team <kernel-team@fb.com>,
	jolsa@kernel.org, Johannes Weiner <hannes@cmpxchg.org>,
	Yonghong Song <yhs@fb.com>
Subject: Re: [RFC bpf-next 0/1] bpf: Add page cache iterator
Date: Thu, 8 Apr 2021 14:33:43 -0700
Message-ID: <CALvZod4kefNWPAwKZdpO8z29sJ2jDh74_C5Y_FSgXFB8s5ZXGA@mail.gmail.com> (raw)
In-Reply-To: <cover.1617831474.git.dxu@dxuuu.xyz>

On Wed, Apr 7, 2021 at 2:47 PM Daniel Xu <dxu@dxuuu.xyz> wrote:
>
> There currently does not exist a way to answer the question: "What is in
> the page cache?". There are various heuristics and counters but nothing
> that can tell you anything like:
>
>   * 3M from /home/dxu/foo.txt
>   * 5K from ...
>   * etc.
>

So, you need the list of inodes for a filesystem that are in memory.
With that list, you can open, map and do mincore on them?

I don't know of a way to get that inode list.

> The answer to the question is particularly useful in the stacked
> container world. Stacked containers implies multiple containers are run
> on the same physical host. Memory is precious resource on some (if not
> most) of these systems. On these systems, it's useful to know how much
> duplicated data is in the page cache. Once you know the answer, you can
> do something about it. One possible technique would be bind mount common
> items from the root host into each container.
>

Oh you want to share page cache between different containers/jobs?
That would complicate charging.

  parent reply index

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-07 21:46 Daniel Xu
2021-04-07 21:46 ` [RFC bpf-next 1/1] bpf: Introduce iter_pagecache Daniel Xu
2021-04-08  6:14   ` Matthew Wilcox
2021-04-08 19:48     ` Daniel Xu
2021-04-08 21:29       ` Matthew Wilcox
2021-04-08  8:19   ` Christian Brauner
2021-04-08 20:44     ` Daniel Xu
2021-04-08 16:45   ` Al Viro
2021-04-08 20:49     ` Daniel Xu
2021-04-08 21:04       ` Al Viro
2021-04-08 22:11   ` Dave Chinner
2021-04-08  7:51 ` [RFC bpf-next 0/1] bpf: Add page cache iterator Christian Brauner
2021-04-08 16:08   ` Daniel Xu
2021-04-08 21:33 ` Shakeel Butt [this message]
2021-04-08 23:13 ` Darrick J. Wong
2021-04-09  0:24   ` Daniel Xu

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