linux-kernel - Re: [PATCH v5 3/4] mm: support large folios swapin as a whole for zRAM-like swapfile

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Message-ID: <ZqcRqxGaJsAwZD3C@casper.infradead.org>
Date: Mon, 29 Jul 2024 04:51:07 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Barry Song <21cnbao@...il.com>
Cc: akpm@...ux-foundation.org, linux-mm@...ck.org, ying.huang@...el.com,
	baolin.wang@...ux.alibaba.com, chrisl@...nel.org, david@...hat.com,
	hannes@...xchg.org, hughd@...gle.com, kaleshsingh@...gle.com,
	kasong@...cent.com, linux-kernel@...r.kernel.org, mhocko@...e.com,
	minchan@...nel.org, nphamcs@...il.com, ryan.roberts@....com,
	senozhatsky@...omium.org, shakeel.butt@...ux.dev,
	shy828301@...il.com, surenb@...gle.com, v-songbaohua@...o.com,
	xiang@...nel.org, yosryahmed@...gle.com,
	Chuanhua Han <hanchuanhua@...o.com>
Subject: Re: [PATCH v5 3/4] mm: support large folios swapin as a whole for
 zRAM-like swapfile

On Fri, Jul 26, 2024 at 09:46:17PM +1200, Barry Song wrote:
> -			folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0,
> -						vma, vmf->address, false);
> +			folio = alloc_swap_folio(vmf);
>  			page = &folio->page;

This is no longer correct.  You need to set 'page' to the precise page
that is being faulted rather than the first page of the folio.  It was
fine before because it always allocated a single-page folio, but now it
must use folio_page() or folio_file_page() (whichever has the correct
semantics for you).

Also you need to fix your test suite to notice this bug.  I suggest
doing that first so that you know whether you've got the calculation
correct.