linux-kernel - Re: [PATCH v5 1/2] mm: store zero pages to be swapped out in a bitmap

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Message-ID: <87ed8zmvla.fsf@linux.intel.com>
Date: Fri, 14 Jun 2024 07:45:37 -0700
From: Andi Kleen <ak@...ux.intel.com>
To: Usama Arif <usamaarif642@...il.com>
Cc: akpm@...ux-foundation.org,  hannes@...xchg.org,  shakeel.butt@...ux.dev,
  david@...hat.com,  ying.huang@...el.com,  hughd@...gle.com,
  willy@...radead.org,  yosryahmed@...gle.com,  nphamcs@...il.com,
  chengming.zhou@...ux.dev,  linux-mm@...ck.org,
  linux-kernel@...r.kernel.org,  kernel-team@...a.com
Subject: Re: [PATCH v5 1/2] mm: store zero pages to be swapped out in a bitmap

Usama Arif <usamaarif642@...il.com> writes:

> Approximately 10-20% of pages to be swapped out are zero pages [1].
> Rather than reading/writing these pages to flash resulting
> in increased I/O and flash wear, a bitmap can be used to mark these
> pages as zero at write time, and the pages can be filled at
> read time if the bit corresponding to the page is set.
> With this patch, NVMe writes in Meta server fleet decreased
> by almost 10% with conventional swap setup (zswap disabled).
>
> [1] https://lore.kernel.org/all/20171018104832epcms5p1b2232e2236258de3d03d1344dde9fce0@epcms5p1/

But how much did the CPU time increase? Surely the new loop is not free?

-Andi