linux-ext4 - Re: [PATCH 2/2] Add batched discard support for ext4

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Date:	Wed, 14 Jul 2010 11:40:56 +0200 (CEST)
From:	Lukas Czerner <lczerner@...hat.com>
To:	Dmitry Monakhov <dmonakhov@...nvz.org>
cc:	Lukas Czerner <lczerner@...hat.com>, eshishki@...hat.com,
	jmoyer@...hat.com, rwheeler@...hat.com, linux-ext4@...r.kernel.org,
	sandeen@...hat.com
Subject: Re: [PATCH 2/2] Add batched discard support for ext4

On Wed, 14 Jul 2010, Dmitry Monakhov wrote:

> Lukas Czerner <lczerner@...hat.com> writes:
> 
> > Walk through each allocation group and trim all free extents. It can be
> > invoked through TRIM ioctl on the file system. The main idea is to
> > provide a way to trim the whole file system if needed, since some SSD's
> > may suffer from performance loss after the whole device was filled (it
> > does not mean that fs is full!).
> >
> > It search fro free extents in each allocation group. When the free
> > extent is found, blocks are marked as used and then trimmed. Afterwards
> > these blocks are marked as free in per-group bitmap.
> Looks ok, except two small notes:
> 1) trim_fs is a time consuming operation and we have to add
>    condresced, and signal_pending checks to allow user to interrupt
>    cmd if necessery. See patch attached.

Hi, Dimitry

thanks for your patch! Although I have one question:


 	for (group = 0; group < ngroups; group++) {
-		int err;
-
-		err = ext4_mb_load_buddy(sb, group, &e4b);
-		if (err) {
+		ret = ext4_mb_load_buddy(sb, group, &e4b);
+		if (ret) {
 			ext4_error(sb, "Error in loading buddy "
 					"information for %u", group);
-			continue;
+			break;
 		}

Is there really need to jump out from the loop and exit in the case of
load_buddy failure ? Next group may very well succeed in loading buddy,
or am I missing something ?

> 2) IMHO runtime trim support is useful sometimes, for example when
>    user really care about data security i.e. unlinked file should be
>    trimmed ASAP. I think we have to provide 'secdel' mount option
>    similar to secdeletion flag for inode, but this is another story
>    not directly connected with the patch.

I like the idea, but IMO this should work for any underlying storage,
not just for SSDs.

Thanks!
-Lukas
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