linux-kernel - Re: [PATCH 5/7] mm: add new 'orders' parameter for find_get_entries() and find_lock

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Date: Mon, 10 Jun 2024 17:59:36 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: akpm@...ux-foundation.org, hughd@...gle.com, david@...hat.com,
	wangkefeng.wang@...wei.com, chrisl@...nel.org, ying.huang@...el.com,
	21cnbao@...il.com, ryan.roberts@....com, shy828301@...il.com,
	ziy@...dia.com, ioworker0@...il.com, da.gomez@...sung.com,
	p.raghav@...sung.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/7] mm: add new 'orders' parameter for
 find_get_entries() and find_lock_entries()

On Thu, Jun 06, 2024 at 07:58:55PM +0800, Baolin Wang wrote:
> In the following patches, shmem will support the swap out of large folios,
> which means the shmem mappings may contain large order swap entries, so an
> 'orders' array is added for find_get_entries() and find_lock_entries() to
> obtain the order size of shmem swap entries, which will help in the release
> of shmem large folio swap entries.

I am not a fan.  I was hoping that 'order' would be encoded in the swap
entry, not passed as a separate parameter.

As I understand it, we currently have a free bit, or
swp_to_radix_entry() would not work.  We can use that as detailed
here to encode the order in a single bit.

https://kernelnewbies.org/MatthewWilcox/NaturallyAlignedOrder