From: Wei Yang <richard.weiyang@gmail.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Wei Yang <richard.weiyang@gmail.com>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/9] XArray: simplify the calculation of shift
Date: Mon, 30 Mar 2020 14:07:12 +0000 [thread overview]
Message-ID: <20200330140712.sloduuoqc5jid64m@master> (raw)
In-Reply-To: <20200330132028.GA22483@bombadil.infradead.org>
On Mon, Mar 30, 2020 at 06:20:28AM -0700, Matthew Wilcox wrote:
>On Mon, Mar 30, 2020 at 12:36:36PM +0000, Wei Yang wrote:
>> When head is NULL, shift is calculated from max. Currently we use a loop
>> to detect how many XA_CHUNK_SHIFT is need to cover max.
>>
>> To achieve this, we can get number of bits max expands and round it up
>> to XA_CHUNK_SHIFT.
>>
>> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
>> ---
>> lib/xarray.c | 6 +-----
>> 1 file changed, 1 insertion(+), 5 deletions(-)
>>
>> diff --git a/lib/xarray.c b/lib/xarray.c
>> index 1d9fab7db8da..6454cf3f5b4c 100644
>> --- a/lib/xarray.c
>> +++ b/lib/xarray.c
>> @@ -560,11 +560,7 @@ static int xas_expand(struct xa_state *xas, void *head)
>> unsigned long max = xas_max(xas);
>>
>> if (!head) {
>> - if (max == 0)
>> - return 0;
>> - while ((max >> shift) >= XA_CHUNK_SIZE)
>> - shift += XA_CHUNK_SHIFT;
>> - return shift + XA_CHUNK_SHIFT;
>> + return roundup(fls_long(max), XA_CHUNK_SHIFT);
>
>This doesn't give the same number. Did you test this?
>
>Consider max = 64. The current code does:
>
>shift = 0;
>64 >> 0 >= 64 (true)
>shift += 6;
>64 >> 6 < 64
>return 12
>
>Your replacement does:
>
>fls_long(64) = 6
fls_long(64) = 7
>roundup(6, 6) is 6.
>
>Please be more careful.
--
Wei Yang
Help you, Help me
next prev parent reply other threads:[~2020-03-30 14:07 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-30 12:36 [PATCH 0/9] XArray: several cleanups Wei Yang
2020-03-30 12:36 ` [PATCH 1/9] XArray: fix comment on Zero/Retry entry Wei Yang
2020-03-30 12:46 ` Matthew Wilcox
2020-03-30 13:42 ` Wei Yang
2020-03-30 12:36 ` [PATCH 2/9] XArray: simplify the calculation of shift Wei Yang
2020-03-30 13:20 ` Matthew Wilcox
2020-03-30 14:07 ` Wei Yang [this message]
2020-03-30 12:36 ` [PATCH 3/9] XArray: handle a NULL head by itself Wei Yang
2020-03-30 12:36 ` [PATCH 4/9] XArray: don't expect to have more nr_values than count Wei Yang
2020-03-30 12:36 ` [PATCH 5/9] XArray: entry in last level is not expected to be a node Wei Yang
2020-03-30 12:48 ` Matthew Wilcox
2020-03-30 14:15 ` Wei Yang
2020-03-30 14:28 ` Matthew Wilcox
2020-03-30 22:10 ` Wei Yang
2020-03-31 13:42 ` Wei Yang
2020-03-31 16:42 ` Matthew Wilcox
2020-03-31 22:04 ` Wei Yang
2020-03-31 23:59 ` Matthew Wilcox
2020-04-01 22:10 ` Wei Yang
2020-04-01 22:20 ` Matthew Wilcox
2020-04-02 12:36 ` Wei Yang
2020-04-03 22:39 ` Wei Yang
2020-04-04 15:37 ` Matthew Wilcox
2020-04-05 11:07 ` Wei Yang
2020-04-05 21:56 ` Matthew Wilcox
2020-04-06 1:14 ` Wei Yang
2020-04-06 1:24 ` Wei Yang
2020-04-11 13:56 ` Wei Yang
2020-04-28 21:24 ` Wei Yang
2020-03-30 12:36 ` [PATCH 6/9] XArray: internal node is a xa_node when it is bigger than XA_ZERO_ENTRY Wei Yang
2020-03-30 12:50 ` Matthew Wilcox
2020-03-30 13:45 ` Wei Yang
2020-03-30 13:49 ` Matthew Wilcox
2020-03-30 14:13 ` Wei Yang
2020-03-30 14:27 ` Matthew Wilcox
2020-03-30 22:20 ` Wei Yang
2020-03-31 0:06 ` Matthew Wilcox
2020-03-31 13:40 ` Wei Yang
2020-03-30 12:36 ` [PATCH 7/9] XArray: the NULL xa_node condition is handled in xas_top Wei Yang
2020-03-30 12:36 ` [PATCH 8/9] XArray: take xas_error() handling for clearer logic Wei Yang
2020-03-30 12:36 ` [PATCH 9/9] XArray: adjust xa_offset till it gets the correct node Wei Yang
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