[Yaffs] GC Usage and Optimization to improve the write perfo…

Hi All,

I'm run into the problem with GC usage in yaffs2, which is causing the lower
write performance.

When the disk(NAND) is in fully erased state(i.e, 0% usage), i will get the
higher write performance,
but as the usage increases, performance is gradually decreases. I am just
trying to copy some files,
delete and then copy again.

I also did an experiment by commenting GC during file write, which leads to
consistently higher
performance. From this its clear that GC is the one which is causing the
problem.

I am thinking of following approaches to address this issue. Please correct
me if i'm wrong

1. I tried the GC during SoftDeleteWorker context. 
    i.e, in the function "yaffs_SoftDeleteChunk" after incrementing the 
"softdeletion" parameter
    of the block information, call yaffs_CheckGarbageCollection

    I have tried this method to minimise the GC load during file write (i.e, 
the load on 
    yaffs_WriteChunkDataToObject)

2. While observed during Garbage Collection that, even if the pagesInUse of 
a block becomes ZERO
    (i.e, bi->pagesInUse - bi->softDeletions in " 
yaffs_FindBlockForGarbageCollection" function,), in 
    function   yaffs_GarbageCollectBlock, we are reading all the chunks and 
decrement the nDataChunks
    counter of the correcponding object. 

    I am just wondering is it possible to remove this overhead (reading all 
the chunks while the pagesInUse
    of that block is zero) by updating the nDataChunks counter while 
softDelete of the corresponding object,
   and erase the block directly while the pagesInUse of that block are zero.

Also i am wondering, will the above two approaches cause any abnormal
behaviour in any other context.

Thanks,
Asif



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