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List:       openldap-technical
Subject:    Re: RSfd in top, memory, etc.
From:       Howard Chu <hyc () symas ! com>
Date:       2023-06-29 16:45:06
Message-ID: 5b341c7e-55e8-cc3c-dcfe-df1063f34cc6 () symas ! com
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Sam Dave wrote:
> While I write to an LMDB database, while it gets bigger and bigger, I can see %MEM \
> in top rising steadily. 
> This is because %MEM is composed of three things, including "RSfd". From the top \
> manpage: 
> RSfd   --   Resident File-Backed Memory Size (KiB)
> A   subset   of resident memory (RES) representing the implicitly shared pages \
> supporting program images and shared libraries. It also includes explicit file \
> mappings, both private and shared. 
> Is it memory mapping that's resulting in the higher RSfd?

LMDB uses shared memory mapped files, so yes.
> 
> RSfd increases do not seem to have an effect on "buff/cache" or "avail Mem", i.e. \
> what most people think as "RAM" is not being used up. I still want to ask, could \
> too high RSfd use result in less efficient use of memory for other programs? I'm \
> essentially wondering how efficient common OSes (e.g. MacOS, Linux) are in this \
> area.

No. The OS can reclaim LMDB's pages (at zero cost) for use by any other program \
whenever memory demands are tight.

> - Sam

-- 
  -- Howard Chu
  CTO, Symas Corp.           http://www.symas.com
  Director, Highland Sun     http://highlandsun.com/hyc/
  Chief Architect, OpenLDAP  http://www.openldap.org/project/


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