linux-kernel - Re: [PATCH v1] Device-mapper(LVM): Convert to use time_after

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Message-ID: <bc1025c5-fa3c-4a49-9d91-d2d90e7423b4@vivo.com>
Date: Fri, 23 Aug 2024 09:18:25 +0000
From: 陈玉凡 <chenyufan@...o.com>
To: Mikulas Patocka <mpatocka@...hat.com>, 陈玉凡
	<chenyufan@...o.com>
CC: Alasdair Kergon <agk@...hat.com>, Mike Snitzer <snitzer@...nel.org>,
	"dm-devel@...ts.linux.dev" <dm-devel@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	opensource.kernel <opensource.kernel@...o.com>
Subject: Re: [PATCH v1] Device-mapper(LVM): Convert to use time_after_eq macro

在 2024/8/23 1:08, Mikulas Patocka 写道:
>
> On Thu, 22 Aug 2024, Chen Yufan wrote:
>
>> Use time_after_eq macro instead of opening it for readability.
>>
>> Signed-off-by: Chen Yufan <chenyufan@...o.com>
>> ---
>>   drivers/md/dm-writecache.c | 5 +++--
>>   1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c
>> index 7ce8847b3..548d4d37e 100644
>> --- a/drivers/md/dm-writecache.c
>> +++ b/drivers/md/dm-writecache.c
>> @@ -16,6 +16,7 @@
>>   #include <linux/pfn_t.h>
>>   #include <linux/libnvdimm.h>
>>   #include <linux/delay.h>
>> +#include <linux/jiffies.h>
>>   #include "dm-io-tracker.h"
>>   
>>   #define DM_MSG_PREFIX "writecache"
>> @@ -1994,8 +1995,8 @@ static void writecache_writeback(struct work_struct *work)
>>   	while (!list_empty(&wc->lru) &&
>>   	       (wc->writeback_all ||
>>   		wc->freelist_size + wc->writeback_size <= wc->freelist_low_watermark ||
>> -		(jiffies - container_of(wc->lru.prev, struct wc_entry, lru)->age >=
>> -		 wc->max_age - wc->max_age / MAX_AGE_DIV))) {
>> +		(time_after_eq(jiffies, container_of(wc->lru.prev, struct wc_entry, lru)->age +
>> +		 (wc->max_age - wc->max_age / MAX_AGE_DIV))))) {
>>   
>>   		n_walked++;
>>   		if (unlikely(n_walked > WRITEBACK_LATENCY) &&
>> -- 
>> 2.39.0
> I'm not sure about this. The old and new code is not really equivalent.
>
> Mikulas

The code here is susceptible to overflow issues, and the time_*() macros 
can handle this.

Chen
>