JFFS2 garbage collector blocking for minutes after mount

Martin Egholm Nielsen martin at egholm-nielsen.dk
Sun Jul 24 16:09:58 EDT 2005

>>47695   idled                   384,63710
>>2997    nand_read_buf           62,43750
>>1122    nand_calculate_ecc      5,84380
>>677     __delay                 33,85000
>>502     nand_do_read_ecc        0,26370
> Right, so we're spending most of that time actually reading the flash.
> If you just read the entire flash device, how long does that take?
>  (time dd if=/dev/mtd0 of=/dev/null) 
This takes some 22 secs - so that explains the half of the time (~45s), 
yes... I guess some of the time has to do with the fact that I used the 
NAND for my root fs - unfortunately also when I did the profiling...

> Artem's patch will improve things further by building up the fragtree
> from newest to oldest node instead of from oldest to newest as we
> currently do -- which actually means we don't need to check the CRC on
> the oldest nodes before they never get added to the tree; we don't
> actually need to read their data payload at all.
Looking forward to the patch leaving the preliminary state...

// Martin

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