linux-kernel - Re: [PATCH] Change the total_dirty from SZ_256M to SZ

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Date:   Sat, 3 Nov 2018 17:17:58 +0800
From:   Qu Wenruo <quwenruo.btrfs@....com>
To:     Nikolay Borisov <nborisov@...e.com>, hmsjwzb <weizhefix@...il.com>
Cc:     clm@...com, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        Omar Sandoval <osandov@...com>,
        Filipe Manana <fdmanana@...e.com>, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Change the total_dirty from SZ_256M to SZ_64M.



On 2018/11/3 下午5:01, Nikolay Borisov wrote:
> 
> 
> On 3.11.18 г. 10:36 ч., hmsjwzb wrote:
>> The SZ_256M will cause trouble in platform with less than 256M memory.
>> For example, a qemu virtual machine.
>>
>> Signed-off-by: hmsjwzb <weizhefix@...il.com>
> 
> If you have actually taken the care to understand the code in
> test_find_delalloc you would have seen that total_dirty and max_bytes
> are actually inter-dependent so you cannot really change total_bytes
> without adjusting max_bytes as well. Otherwise tests will start breaking.

Nowadays even for VM, the memory size should start from 2G.
If this 256M is causing problem, one should really re-consider the
memory size of the VM.

Not to mention the magic number is two ensure we have at least 2 file
extents.

> 
> NACK on this (and likely any future postings of this) since the tests
> are sized in a such a way so as to test design limits (such as the max
> extent size which is 128MB)

And we should add some comment about this.

Personally I prefer some comment with this and also use (2 *
BTRFS_MAX_EXTENT_SIZE) other than this intermediate number.

Thanks,
Qu

> 
> 
>> ---
>>  fs/btrfs/tests/extent-io-tests.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/btrfs/tests/extent-io-tests.c b/fs/btrfs/tests/extent-io-tests.c
>> index 9e0f4a01be14..cb23dce96a2d 100644
>> --- a/fs/btrfs/tests/extent-io-tests.c
>> +++ b/fs/btrfs/tests/extent-io-tests.c
>> @@ -62,7 +62,7 @@ static int test_find_delalloc(u32 sectorsize)
>>  	struct page *page;
>>  	struct page *locked_page = NULL;
>>  	unsigned long index = 0;
>> -	u64 total_dirty = SZ_256M;
>> +	u64 total_dirty = SZ_64M;
>>  	u64 max_bytes = SZ_128M;
>>  	u64 start, end, test_start;
>>  	u64 found;
>>