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blk_cgroup_congested() walks the current task's blkcg ancestor chain on every readahead decision and, once swap is in use, on every anonymous and shmem folio allocation. The answer is almost always "no", but finding that out costs two loads per level on two cold cache lines, plus an out-of-line kthread_blkcg() and an RCU read-side pair. On a fleet profile of hosts running containers with 5-10 level hierarchies it costs about as much as all of mutex_lock(), 99.4% of it under __folio_throttle_swaprate(). Gate the walk on a global count of blkcgs with a non-zero congestion_count. The counter only moves on the 0 <-> 1 transitions of each blkcg's congestion_count, so the extra atomic stays in the throttle arm/disarm paths and never appears in steady state. When something is throttled the counter is non-zero and the walk runs as before. Signed-off-by: Usama Arif <usama.arif@linux.dev> Acked-by: Tejun Heo <tj@kernel.org> Link: https://patch.msgid.link/20260814165712.510132-4-usama.arif@linux.dev Signed-off-by: Jens Axboe <axboe@kernel.dk> |
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| acpi | ||
| asm-generic | ||
| clocksource | ||
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| cxl | ||
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| dt-bindings | ||
| hyperv | ||
| keys | ||
| kunit | ||
| kvm | ||
| linux | ||
| math-emu | ||
| media | ||
| memory | ||
| misc | ||
| net | ||
| pcmcia | ||
| ras | ||
| rdma | ||
| rv | ||
| scsi | ||
| soc | ||
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| target | ||
| trace | ||
| uapi | ||
| ufs | ||
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| xen | ||
| Kbuild | ||