[OpenWrt-Devel] uci commit bumping amount of dentry active slab objects

[Rafał Miłecki]

I was looking at slabinfo and noticed something about uci. Executing
"uci commit" increases amount of "dentry" active objects.

# echo 2 > /proc/sys/vm/drop_caches

# egrep "dentry|kmalloc-64" /proc/slabinfo
dentry               559   2040    136   30    1 : tunables  120   60    8 : sla
kmalloc-64          5357   9324     64   63    1 : tunables  120   60    8 : sla

# for N in `seq 1 1 1000`; do uci commit network; done

# egrep "dentry|kmalloc-64" /proc/slabinfo
dentry              3540   3540    136   30    1 : tunables  120   60    8 : sla
kmalloc-64          6457   9324     64   63    1 : tunables  120   60    8 : sla

# for N in `seq 1 1 1000`; do uci commit network; done

# egrep "dentry|kmalloc-64" /proc/slabinfo
dentry              6570   6570    136   30    1 : tunables  120   60    8 : sla
kmalloc-64          7587   9324     64   63    1 : tunables  120   60    8 : sla

This is not critical. As you know Linux kernel loves caching. When
amount of free RAM goes below ~2 MiB I can see kernel freeing dentry
objects and it doesn't OOM.

But I'm still wondering if everything is OK. Is this normal kernel
keeps increasing pool of dentry objects as the result of "uci commit"
command?

I expected "uci command" first to bump amount of active and total
dentry objects. Then when uci exits I expected amount of active
objects to go down. Kernel could reuse inactive objects during next
"uci commit" call. In such scenario amount of active objects would
vary, but amount of total object would be more-or-less stable.

Can we be missing some (f)close in UCI? I checked uci_file_commit and
it looks alright. Or is this just how the filesystem works? I'm using
3.18.21 (OpenWrt 15.05 branch) on device with serial flash (so JFFS2).

-- 
Rafał
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