ZFS L2ARC compression buffer leak

[nielsdec]

There seems to be a slight memory leak when using l2ARC compression, the temporary data buffer which holds the compressed data is not always freed.

This was tested by adding an extra entry in arcstats, which keeps track of the data allocated for temporary buffers. This slowly keeps increasing (besides the alloc/dealloc fluctuations), which implies a memory leak.

I think the path is:

1. buffer allocated in l2arc_compress_buf
2. arc entry removed/being removed before l2arc_write_done can free the buffer.

In any case arc_hdr_destroy will free the l2arc_buf_hdr without checking if the temp buffer is used/freeing the temp buffer. So if it's allocated at that point it will never be released.

I see if I can make a patch.

[behlendorf]

Add reference to upstream issue:

https://www.illumos.org/issues/3995

[ryao]

danmcd has merged Saso's patch into illumos-gate in illumos/illumos-gate@e4be62a. I will pull it into my pull request #1775 shortly.

[ryao]

I seem to have made a mistake. The fix for this issue was Illumos 3995. What was merged into illumos-gate was Illumos 3964. I mislabeled Illumos 3995 as Illumos 3964 and included this in my Gentoo patches (and had planned to refresh #1775 with this). I will fix my mistake when I fresh #1775, but please disregard my previous comment.