| Message ID | 1545428420-126557-1-git-send-email-yang.shi@linux.alibaba.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v3,1/2] mm: swap: check if swap backing device is congested or not | expand |
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>
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.
On Sat, 22 Dec 2018 05:40:19 +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. > > 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. Some words about the observed effects of the patch would be more than appropriate!
On 12/28/18 4:42 PM, Andrew Morton wrote: > On Sat, 22 Dec 2018 05:40:19 +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. >> >> 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. > Some words about the observed effects of the patch would be more than > appropriate! Yes, sure. Actually, this could reduce the latency long tail of do_swap_page() on a congested system. The test on my virtual machine with emulated HDD shows: Without swap congestion check: page_fault1_thr-1490 [023] 129.311706: funcgraph_entry: # 57377.796 us | do_swap_page(); page_fault1_thr-1490 [023] 129.369103: funcgraph_entry: 5.642 us | do_swap_page(); page_fault1_thr-1490 [023] 129.369119: funcgraph_entry: # 1289.592 us | do_swap_page(); page_fault1_thr-1490 [023] 129.370411: funcgraph_entry: 4.957 us | do_swap_page(); page_fault1_thr-1490 [023] 129.370419: funcgraph_entry: 1.940 us | do_swap_page(); page_fault1_thr-1490 [023] 129.378847: funcgraph_entry: # 1411.385 us | do_swap_page(); page_fault1_thr-1490 [023] 129.380262: funcgraph_entry: 3.916 us | do_swap_page(); page_fault1_thr-1490 [023] 129.380275: funcgraph_entry: # 4287.751 us | do_swap_page(); With swap congestion check: runtest.py-1417 [020] 301.925911: funcgraph_entry: # 9870.146 us | do_swap_page(); runtest.py-1417 [020] 301.935785: funcgraph_entry: 9.802 us | do_swap_page(); runtest.py-1417 [020] 301.935799: funcgraph_entry: 3.551 us | do_swap_page(); runtest.py-1417 [020] 301.935806: funcgraph_entry: 2.142 us | do_swap_page(); runtest.py-1417 [020] 301.935853: funcgraph_entry: 6.938 us | do_swap_page(); runtest.py-1417 [020] 301.935864: funcgraph_entry: 3.765 us | do_swap_page(); runtest.py-1417 [020] 301.935871: funcgraph_entry: 3.600 us | do_swap_page(); runtest.py-1417 [020] 301.935878: funcgraph_entry: 7.202 us | do_swap_page(); The long tail latency (>1000us) is reduced significantly. BTW, do you need I resend the patch with the above information appended into the commit log? Thanks, Yang
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;
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(+)