Hi Neil,
you are completely right. I got confused between mddev->recovery_cp
and sb->resync_offset; the latter may become 0 due to in-flight WRITEs
and not due to resync. Looking at the code again, I see that
recovery_cp is totally one-way from sb->resync_offset to MaxSector
(except for explicit loading via sysfs). Also recovery_cp is not
relevant to "check" and "repair". So recovery_cp is pretty simple
after all.
Below is V2 patch. (I have also to credit it to somebody else, because
he was the one that said - just do rcw while you are resyncing).
Thanks,
Alex.
-----------------
>From cc3e2bfcf2fd2c69180577949425d69de88706bb Mon Sep 17 00:00:00 2001
From: Alex Lyakas <alex@xxxxxxxxxxxxxxxxx>
Date: Thu, 13 Sep 2012 18:55:00 +0300
Subject: [PATCH] When RAID5 is dirty, force reconstruct-write instead of
read-modify-write.
Signed-off-by: Alex Lyakas <alex@xxxxxxxxxxxxxxxxx>
Signed-off-by: Yair Hershko <yair@xxxxxxxxxxxxxxxxx>
diff --git a/ubuntu_kmodules/Ubuntu-3.2.0-25.40/drivers/md/raid5.c
b/ubuntu_kmodules/Ubuntu-3.2.0-25.40/drivers/md/raid5.c
index 5332202..9fdd5e3 100644
--- a/ubuntu_kmodules/Ubuntu-3.2.0-25.40/drivers/md/raid5.c
+++ b/ubuntu_kmodules/Ubuntu-3.2.0-25.40/drivers/md/raid5.c
@@ -2555,12 +2555,24 @@ static void handle_stripe_dirtying(struct r5conf *conf,
int disks)
{
int rmw = 0, rcw = 0, i;
- if (conf->max_degraded == 2) {
- /* RAID6 requires 'rcw' in current implementation
- * Calculate the real rcw later - for now fake it
+ sector_t recovery_cp = conf->mddev->recovery_cp;
+
+ /* RAID6 requires 'rcw' in current implementation.
+ * Otherwise, check whether resync is now happening or should start.
+ * If yes, then the array is dirty (after unclean shutdown or
+ * initial creation), so parity in some stripes might be inconsistent.
+ * In this case, we need to always do reconstruct-write, to ensure
+ * that in case of drive failure or read-error correction, we
+ * generate correct data from the parity.
+ */
+ if (conf->max_degraded == 2 ||
+ (recovery_cp < MaxSector && sh->sector >= recovery_cp)) {
+ /* Calculate the real rcw later - for now make it
* look like rcw is cheaper
*/
rcw = 1; rmw = 2;
+ pr_debug("force RCW max_degraded=%u, recovery_cp=%lu
sh->sector=%lu\n",
+ conf->max_degraded, recovery_cp, sh->sector);
} else for (i = disks; i--; ) {
/* would I have to read this buffer for read_modify_write */
struct r5dev *dev = &sh->dev[i];
On Wed, Sep 19, 2012 at 8:59 AM, NeilBrown <neilb@xxxxxxx> wrote:
> On Mon, 17 Sep 2012 14:15:16 +0300 Alexander Lyakas <alex.bolshoy@xxxxxxxxx>
> wrote:
>
>> Hi Neil,
>> below is a bit less-ugly version of the patch.
>> Thanks,
>> Alex.
>>
>> >From 05cf800d623bf558c99d542cf8bf083c85b7e5d5 Mon Sep 17 00:00:00 2001
>> From: Alex Lyakas <alex@xxxxxxxxxxxxxxxxx>
>> Date: Thu, 13 Sep 2012 18:55:00 +0300
>> Subject: [PATCH] When RAID5 is dirty, force reconstruct-write instead of
>> read-modify-write.
>>
>> Signed-off-by: Alex Lyakas <alex@xxxxxxxxxxxxxxxxx>
>> Signed-off-by: Yair Hershko <yair@xxxxxxxxxxxxxxxxx>
>>
>> diff --git a/ubuntu_kmodules/Ubuntu-3.2.0-25.40/drivers/md/raid5.c
>> b/ubuntu_kmodules/Ubuntu-3.2.0-25.40/drivers/md/raid5.c
>> index 5332202..0702785 100644
>> --- a/ubuntu_kmodules/Ubuntu-3.2.0-25.40/drivers/md/raid5.c
>> +++ b/ubuntu_kmodules/Ubuntu-3.2.0-25.40/drivers/md/raid5.c
>> @@ -2555,12 +2555,36 @@ static void handle_stripe_dirtying(struct r5conf *conf,
>> int disks)
>> {
>> int rmw = 0, rcw = 0, i;
>> - if (conf->max_degraded == 2) {
>> - /* RAID6 requires 'rcw' in current implementation
>> - * Calculate the real rcw later - for now fake it
>> + sector_t recovery_cp = conf->mddev->recovery_cp;
>> + unsigned long recovery = conf->mddev->recovery;
>> + int needed = test_bit(MD_RECOVERY_NEEDED, &recovery);
>> + int resyncing = test_bit(MD_RECOVERY_SYNC, &recovery) &&
>> + !test_bit(MD_RECOVERY_REQUESTED, &recovery) &&
>> + !test_bit(MD_RECOVERY_CHECK, &recovery);
>> + int transitional = test_bit(MD_RECOVERY_RUNNING, &recovery) &&
>> + !test_bit(MD_RECOVERY_SYNC, &recovery) &&
>> + !test_bit(MD_RECOVERY_RECOVER, &recovery) &&
>> + !test_bit(MD_RECOVERY_DONE, &recovery) &&
>> + !test_bit(MD_RECOVERY_RESHAPE, &recovery);
>
> Thanks Alex,
> however I don't understand why you want to test all of these bits.
> Isn't it enough just to check ->recovery_cp ??
>
>> +
>> + /* RAID6 requires 'rcw' in current implementation.
>> + * Otherwise, attempt to check whether resync is now happening
>> + * or should start.
>> + * If yes, then the array is dirty (after unclean shutdown or
>> + * initial creation), so parity in some stripes might be inconsistent.
>> + * In this case, we need to always do reconstruct-write, to ensure
>> + * that in case of drive failure or read-error correction, we
>> + * generate correct data from the parity.
>> + */
>> + if (conf->max_degraded == 2 ||
>> + (recovery_cp < MaxSector && sh->sector >= recovery_cp &&
>> + (needed || resyncing || transitional))) {
>> + /* Calculate the real rcw later - for now fake it
>> * look like rcw is cheaper
>
> Also, we should probably fix this comment. s/fake/make/
>
> Thanks,
> NeilBrown
>
>
>
>> */
>> rcw = 1; rmw = 2;
>> + pr_debug("force RCW max_degraded=%u, recovery_cp=%lu
>> sh->sector=%lu recovery=0x%lx\n",
>> + conf->max_degraded, recovery_cp, sh->sector, recovery);
>> } else for (i = disks; i--; ) {
>> /* would I have to read this buffer for read_modify_write */
>> struct r5dev *dev = &sh->dev[i];
>
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