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mm: swapfile: check usable swap device in __folio_throttle_swaprate()

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Skip blk_cgroup_congested() if there is no usable swap device since no
swapin/out will occur, Thereby avoid taking swap_lock.  The difference
is shown below from perf date of CoW pagefault,

  perf report -g -i perf.data.swapon  | egrep "blk_cgroup_congested|__folio_throttle_swaprate"
      1.01%     0.16%  page_fault2_pro  [kernel.kallsyms]      [k] __folio_throttle_swaprate
      0.83%     0.80%  page_fault2_pro  [kernel.kallsyms]      [k] blk_cgroup_congested

  perf report -g -i perf.data.swapoff   | egrep  "blk_cgroup_congested|__folio_throttle_swaprate"
      0.15%     0.15%  page_fault2_pro  [kernel.kallsyms]      [k] __folio_throttle_swaprate

Link: https://lkml.kernel.org/r/20240418135644.2736748-1-wangkefeng.wang@huawei.com
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Kefeng Wang 2024-04-18 21:56:44 +08:00 committed by Andrew Morton
parent d21f996b02
commit 80e7502148
1 changed files with 10 additions and 3 deletions
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13
mm/swapfile.c
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@ -2444,13 +2444,17 @@ static void reinsert_swap_info(struct swap_info_struct *p)
spin_unlock(&swap_lock);
}
static bool __has_usable_swap(void)
{
return !plist_head_empty(&swap_active_head);
}
bool has_usable_swap(void)
{
bool ret = true;
bool ret;
spin_lock(&swap_lock);
if (plist_head_empty(&swap_active_head))
ret = false;
ret = __has_usable_swap();
spin_unlock(&swap_lock);
return ret;
}
@ -3710,6 +3714,9 @@ void __folio_throttle_swaprate(struct folio *folio, gfp_t gfp)
if (!(gfp & __GFP_IO))
return;
if (!__has_usable_swap())
return;
if (!blk_cgroup_congested())
return;