Hi,

There is a bug in YAFFS2 in GC implementation.

While checking the block, whether its qualified for GC(in the function yaffs_BlockNotDisqualifiedFromGC), we are supposed to find the oldest dirty sequence number. But in the present implementation, we are finding only the oldest sequence number.

Hence, it needs to be changed to find the oldest dirty sequence number as under.

Current Implementation

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"if (b->blockState == YAFFS_BLOCK_STATE_FULL && (b->pagesInUse - b->softDeletions) < dev->nChunksPerBlock && b->sequenceNumber < seq)"

Required Implementation(To find Oldest Dirty Sequence Number)

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"if (b->blockState == YAFFS_BLOCK_STATE_FULL && (b->pagesInUse - b->softDeletions) <= (bi->pagesInUse - bi->softDeletions) && b->sequenceNumber < seq)"

After disk is been used for long time(multiple usages), even if the disk has the valid Block for the GC having sequence number newer than the oldest sequence number, then this block is not qualified for GC(with Current Implementation). This also leads to poor write performance...

I have tested with the modified implementation, and is working consistantly fine with proper disk usage and also with improved write performance.

Hope this makes sense...

Regards,

Asif

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