Messages in this thread | | | Date | Thu, 10 Jan 2019 15:31:47 -0800 | From | Andrew Morton <> | Subject | Re: [v5 PATCH 1/2] mm: swap: check if swap backing device is congested or not |
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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)) {
I re-read your discussion with Tim and I must say the reasoning behind this test remain foggy.
What goes wrong if we just remove it?
What is the status of shmem swap readahead?
Can we at least get a comment in here which explains the reasoning?
Thanks.
> + 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. */
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