linux-kernel - Re: [PATCH v6 2/2] mm: support large folios swap-in for zRAM-like devices

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Message-ID: <Zr_BydCiQInI0ZMz@casper.infradead.org>
Date: Fri, 16 Aug 2024 22:16:57 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Barry Song <21cnbao@...il.com>
Cc: wangkefeng.wang@...wei.com, akpm@...ux-foundation.org,
	baolin.wang@...ux.alibaba.com, chrisl@...nel.org, david@...hat.com,
	hanchuanhua@...o.com, hannes@...xchg.org, hch@...radead.org,
	hughd@...gle.com, kaleshsingh@...gle.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, mhocko@...e.com,
	minchan@...nel.org, nphamcs@...il.com, ryan.roberts@....com,
	ryncsn@...il.com, senozhatsky@...omium.org, shakeel.butt@...ux.dev,
	shy828301@...il.com, surenb@...gle.com, v-songbaohua@...o.com,
	xiang@...nel.org, ying.huang@...el.com, yosryahmed@...gle.com
Subject: Re: [PATCH v6 2/2] mm: support large folios swap-in for zRAM-like
 devices

On Fri, Aug 16, 2024 at 11:06:12AM +1200, Barry Song wrote:
> When memcg approaches its limit, charging mTHP becomes difficult.
> At this point, when the charge fails, we fallback to the next order
> to avoid repeatedly retrying larger orders.

Why do you always find the ugliest possible solution to a problem?

> @@ -4244,7 +4248,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>  				}
>  				need_clear_cache = true;
>  
> -				if (mem_cgroup_swapin_charge_folio(folio,
> +				if (nr_pages == 1 && mem_cgroup_swapin_charge_folio(folio,
>  							vma->vm_mm, GFP_KERNEL,
>  							entry)) {
>  					ret = VM_FAULT_OOM;

Just make alloc_swap_folio() always charge the folio, even for order-0.

And you'll have to uncharge it in the swapcache_prepare() failure case.