Re: [v3 PATCH 1/2] mm: swap: check if swap backing device is congested or not

[Yang Shi <yang.shi@linux.alibaba.com>]

On 12/21/18 2:42 PM, Tim Chen wrote:
> On 12/21/18 1:40 PM, Yang Shi wrote:
>> Swap readahead would read in a few pages regardless if the underlying
>> device is busy or not.  It may incur long waiting time if the device is
>> congested, and it may also exacerbate the congestion.
>>
>> Use inode_read_congested() to check if the underlying device is busy or
>> not like what file page readahead does.  Get inode from swap_info_struct.
>> Although we can add inode information in swap_address_space
>> (address_space->host), it may lead some unexpected side effect, i.e.
>> it may break mapping_cap_account_dirty().  Using inode from
>> swap_info_struct seems simple and good enough.
>>
>> Just does the check in vma_cluster_readahead() since
>> swap_vma_readahead() is just used for non-rotational device which
>> much less likely has congestion than traditional HDD.
>>
>> Although swap slots may be consecutive on swap partition, it still may be
>> fragmented on swap file. This check would help to reduce excessive stall
>> for such case.
>>
>> Cc: Huang Ying <ying.huang@intel.com>
>> Cc: Tim Chen <tim.c.chen@intel.com>
>> Cc: Minchan Kim <minchan@kernel.org>
>> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
>> ---
>> v3: Move inode deference under swap device type check per Tim Chen
>> v2: Check the swap device type per Tim Chen
>>
>>   mm/swap_state.c | 7 +++++++
>>   1 file changed, 7 insertions(+)
>>
>> diff --git a/mm/swap_state.c b/mm/swap_state.c
>> index fd2f21e..78d500e 100644
>> --- a/mm/swap_state.c
>> +++ b/mm/swap_state.c
>> @@ -538,11 +538,18 @@ struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
>>   	bool do_poll = true, page_allocated;
>>   	struct vm_area_struct *vma = vmf->vma;
>>   	unsigned long addr = vmf->address;
>> +	struct inode *inode = NULL;
>>   
>>   	mask = swapin_nr_pages(offset) - 1;
>>   	if (!mask)
>>   		goto skip;
>>   
>> +	if (si->flags & (SWP_BLKDEV | SWP_FS)) {
>> +		inode = si->swap_file->f_mapping->host;
>> +		if (inode_read_congested(inode))
>> +			goto skip;
>> +	}
>> +
>>   	do_poll = false;
>>   	/* Read a page_cluster sized and aligned cluster around offset. */
>>   	start_offset = offset & ~mask;
>>
> Acked-by: Tim Chen <tim.c.chen@linux.intel.com>

Thanks. Happy holiday.