linux-kernel - Re: [PATCH v2] mm: shmem: skip swapcache for swapin of synchronous swap device

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Message-ID: <Z3aQKm5_s-5XkAK7@casper.infradead.org>
Date: Thu, 2 Jan 2025 13:10:02 +0000
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, kasong@...cent.com,
	ying.huang@...ux.alibaba.com, 21cnbao@...il.com,
	ryan.roberts@....com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm: shmem: skip swapcache for swapin of synchronous
 swap device

On Thu, Jan 02, 2025 at 04:40:17PM +0800, Baolin Wang wrote:
> With fast swap devices (such as zram), swapin latency is crucial to applications.
> For shmem swapin, similar to anonymous memory swapin, we can skip the swapcache
> operation to improve swapin latency.

OK, but now we have more complexity.  Why can't we always skip the
swapcache on swapin?  (Actually, I think we can always skip the
swapcache on swapout too, but that's a different matter).

> +static struct folio *shmem_swap_alloc_folio(struct inode *inode, struct vm_area_struct *vma,
> +					    pgoff_t index, swp_entry_t entry, int order, gfp_t gfp)

Please wrap at 80 columns and use two tabs for indenting subsequent
lines.  ie:

static struct folio *shmem_swap_alloc_folio(struct inode *inode,
		struct vm_area_struct *vma, pgoff_t index, swp_entry_t entry,
		int order, gfp_t gfp)