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Subject[PATCH] proc: do less stuff under ->pde_unload_lock
Commit ca469f35a8e9ef12571a4b80ac6d7fdc0260fb44
("deal with races between remove_proc_entry() and proc_reg_release()")
moved too much stuff under ->pde_unload_lock making a problem described
at series "[PATCH v5] procfs: Improve Scaling in proc" worse.

While RCU is being figured out, move kfree() out of ->pde_unload_lock.

On my potato, difference is only 0.5% speedup with concurrent
open+read+close of /proc/cmdline, but the effect should be more
noticeable on more capable machines.

$ perf stat -r 16 -- ./proc-j 16

Performance counter stats for './proc-j 16' (16 runs):

130569.502377 task-clock (msec) # 15.872 CPUs utilized ( +- 0.05% )
19,169 context-switches # 0.147 K/sec ( +- 0.18% )
15 cpu-migrations # 0.000 K/sec ( +- 3.27% )
437 page-faults # 0.003 K/sec ( +- 1.25% )
300,172,097,675 cycles # 2.299 GHz ( +- 0.05% )
96,793,267,308 instructions # 0.32 insn per cycle ( +- 0.04% )
22,798,342,298 branches # 174.607 M/sec ( +- 0.04% )
111,764,687 branch-misses # 0.49% of all branches ( +- 0.47% )

8.226574400 seconds time elapsed ( +- 0.05% )
^^^^^^^^^^^


$ perf stat -r 16 -- ./proc-j 16

Performance counter stats for './proc-j 16' (16 runs):

129866.777392 task-clock (msec) # 15.869 CPUs utilized ( +- 0.04% )
19,154 context-switches # 0.147 K/sec ( +- 0.66% )
14 cpu-migrations # 0.000 K/sec ( +- 1.73% )
431 page-faults # 0.003 K/sec ( +- 1.09% )
298,556,520,546 cycles # 2.299 GHz ( +- 0.04% )
96,525,366,833 instructions # 0.32 insn per cycle ( +- 0.04% )
22,730,194,043 branches # 175.027 M/sec ( +- 0.04% )
111,506,074 branch-misses # 0.49% of all branches ( +- 0.18% )

8.183629778 seconds time elapsed ( +- 0.04% )
^^^^^^^^^^^

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

fs/proc/inode.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)

--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -138,7 +138,7 @@ static void unuse_pde(struct proc_dir_entry *pde)
complete(pde->pde_unload_completion);
}

-/* pde is locked */
+/* pde is locked on entry, unlocked on exit */
static void close_pdeo(struct proc_dir_entry *pde, struct pde_opener *pdeo)
{
/*
@@ -157,9 +157,10 @@ static void close_pdeo(struct proc_dir_entry *pde, struct pde_opener *pdeo)
pdeo->c = &c;
spin_unlock(&pde->pde_unload_lock);
wait_for_completion(&c);
- spin_lock(&pde->pde_unload_lock);
} else {
struct file *file;
+ struct completion *c;
+
pdeo->closing = true;
spin_unlock(&pde->pde_unload_lock);
file = pdeo->file;
@@ -167,8 +168,10 @@ static void close_pdeo(struct proc_dir_entry *pde, struct pde_opener *pdeo)
spin_lock(&pde->pde_unload_lock);
/* After ->release. */
list_del(&pdeo->lh);
- if (unlikely(pdeo->c))
- complete(pdeo->c);
+ c = pdeo->c;
+ spin_unlock(&pde->pde_unload_lock);
+ if (unlikely(c))
+ complete(c);
kfree(pdeo);
}
}
@@ -188,6 +191,7 @@ void proc_entry_rundown(struct proc_dir_entry *de)
struct pde_opener *pdeo;
pdeo = list_first_entry(&de->pde_openers, struct pde_opener, lh);
close_pdeo(de, pdeo);
+ spin_lock(&de->pde_unload_lock);
}
spin_unlock(&de->pde_unload_lock);
}
@@ -375,7 +379,7 @@ static int proc_reg_release(struct inode *inode, struct file *file)
list_for_each_entry(pdeo, &pde->pde_openers, lh) {
if (pdeo->file == file) {
close_pdeo(pde, pdeo);
- break;
+ return 0;
}
}
spin_unlock(&pde->pde_unload_lock);
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