Re: [v5 PATCH 1/2] mm: swap: check if swap backing device is congested or not

Andrew Morton
2019-01-10T23:20:31Z

On Fri, 4 Jan 2019 03:27:52 +0800 Yang Shi <yang.shi@linux.alibaba.com> 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.
>
> ...
>
> --- 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;

Neater:

--- a/mm/swap_state.c~mm-swap-check-if-swap-backing-device-is-congested-or-not-fix
+++ a/mm/swap_state.c
@@ -538,14 +538,13 @@ struct page *swap_cluster_readahead(swp_
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;
+ struct inode *inode = si->swap_file->f_mapping->host;
if (inode_read_congested(inode))
goto skip;
}
_