linux-kernel - Re: [PATCH 2/6] mm/page_io: use a folio in sio_read

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Date:   Tue, 18 Jul 2023 20:58:17 +0800
From:   "zhangpeng (AS)" <zhangpeng362@...wei.com>
To:     Matthew Wilcox <willy@...radead.org>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <sidhartha.kumar@...cle.com>, <akpm@...ux-foundation.org>,
        <wangkefeng.wang@...wei.com>, <sunnanyong@...wei.com>,
        Kent Overstreet <kent.overstreet@...il.com>
Subject: Re: [PATCH 2/6] mm/page_io: use a folio in sio_read_complete()

On 2023/7/17 21:40, Matthew Wilcox wrote:

> On Mon, Jul 17, 2023 at 09:25:58PM +0800, Peng Zhang wrote:
>> +++ b/mm/page_io.c
>> @@ -406,19 +406,19 @@ static void sio_read_complete(struct kiocb *iocb, long ret)
>>   
>>   	if (ret == sio->len) {
>>   		for (p = 0; p < sio->pages; p++) {
>> -			struct page *page = sio->bvec[p].bv_page;
>> +			struct folio *folio = page_folio(sio->bvec[p].bv_page);
>>   
>> -			SetPageUptodate(page);
>> -			unlock_page(page);
>> +			folio_mark_uptodate(folio);
>> +			folio_unlock(folio);
>>   		}
> I'm kind of shocked this works today.  Usually bvecs coalesce adjacent
> pages into a single entry, so you need to use a real iterator like
> bio_for_each_folio_all() to extract individual pages from a bvec.
> Maybe the sio bvec is constructed inefficiently.
>
> I think Kent had some bvec folio iterators in progress?

I'll convert bio_first_page_all() to bio_first_folio_all() in a v2.

>>   		count_vm_events(PSWPIN, sio->pages);
>>   	} else {
>>   		for (p = 0; p < sio->pages; p++) {
>> -			struct page *page = sio->bvec[p].bv_page;
>> +			struct folio *folio = page_folio(sio->bvec[p].bv_page);
>>   
>> -			SetPageError(page);
>> -			ClearPageUptodate(page);
>> -			unlock_page(page);
>> +			folio_set_error(folio);
>> +			folio_clear_uptodate(folio);
>> +			folio_unlock(folio);
> Similar questions to the last patch -- who checks the error flag on this
> page/folio, and isn't the folio already !uptodate?

Yes, the folio is already !uptodate. I'll drop this line.
Maybe wait_dev_supers() in fs/btrfs/disk-io.c checks the PageError()?

>>   		}
>>   		pr_alert_ratelimited("Read-error on swap-device\n");
>>   	}
>> -- 
>> 2.25.1
>>
>
-- 
Best Regards,
Peng