Date: Thu, 09 Dec 2010 16:19:05 +0100 From: Luca Pizzamiglio <l.pizzamiglio@bally-wulff.de> To: freebsd-fs@freebsd.org Subject: Softupdate on UFS and "sometimes" slow flash disk Message-ID: <4D00F369.90004@bally-wulff.de>
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Hi list,
I'm writing here, hoping this is the right list.
We're using a PC with a Flash PATA module (4GB, non properly a SSD).
The disk is 2.8 GB used (more or less) and the root partition is around
3.8 GB.
During the update/restore procedure (based on restore(8)) I encountered
a "disk full message" when the procedure is around 1 GB. After this
message, the procedure continues without any other problem. At the end,
disk has, as usual, 1 GB available space.
I investigate deeply the problem and I monitored the
softdep_request_cleanup() function that frees pending blocks. In one
case of my scenario it return without freeing nothing, but there are a
lot of free pending blocks.
After further analysis I discovered that my flash module sometimes is
dramatically slow (I don't know what the controller is doing...).
softdep_request_cleanup() implements a time control system. Before to
free blocks, it invokes ffs_update() in a blocking manner. On my
"sometimes" slow flash module this ffs_update() takes more than 2
seconds and softdep_request_cleanup() return without freeing.
Other invocations are not so slow and everything is fine.
I know that probably there is some problem inside my flash module, but I
guess that the initialization of the time control mechanism should be
made after the ffs_update().
I propose here a patch, that should correct that behavior.
Best regards
Luca Pizzamiglio
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Index: ffs_softdep.c
===================================================================
--- ffs_softdep.c (revision 3162)
+++ ffs_softdep.c (working copy)
@@ -5796,7 +5796,6 @@
ump = VTOI(vp)->i_ump;
mtx_assert(UFS_MTX(ump), MA_OWNED);
needed = fs->fs_cstotal.cs_nbfree + fs->fs_contigsumsize;
- starttime = time_second + tickdelay;
/*
* If we are being called because of a process doing a
* copy-on-write, then it is not safe to update the vnode
@@ -5809,6 +5808,7 @@
if (error != 0)
return (0);
}
+ starttime = time_second + tickdelay;
while (fs->fs_pendingblocks > 0 && fs->fs_cstotal.cs_nbfree <= needed) {
if (time_second > starttime)
return (0);
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