> -----Original Message----- > From: Arnd Bergmann [mailto:arnd@xxxxxxxx] > Sent: Saturday, February 12, 2011 4:38 PM > To: Dong, Chuanxiao > Cc: linux-mmc@xxxxxxxxxxxxxxx; cjb@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > akpm@xxxxxxxxxxxxxxxxxxxx; adrian.hunter@xxxxxxxxx > Subject: Re: [PATCH v4 1/3]mmc: set max_discard_sectors value for mmc queue > > On Saturday 12 February 2011 07:22:14 Chuanxiao Dong wrote: > > max_discard_sectors value is UINT_MAX which means kernel block layer can pass > > down unlimited sectors to MMC driver to erase. But erasing so many sectors may > > delay some other important I/O requests. This is not preferred. > > > > So use 'pref_erase' to set a suitable max_discard_sectors value for mmc queue to > > avoid erasing too many sectors at one time. > > > > Signed-off-by: Chuanxiao Dong <chuanxiao.dong@xxxxxxxxx> > > I'm not sure about this one. pref_erase on SDHC cards should be the *minimum* > unit you can erase in one request, not the maximum. Erasing an arbitrary Hi Arnd, I found the comment in mmc_init_erase() function which explains the 'pref_erase': 'pref_erase' is defined as a guide to limit erases to that size and alignment. So I think it is not the minimum unit driver can erase, also not the maximum erase unit. It just a guide erase size for driver which can avoid holding host controller too long to response other I/O requests. > number of allocation units on an SDHC card should complete almost instantly, > because it only needs to update a single table with the allocation units. > > Discarding partial allocation units will take a lot longer, because the > card then has to copy over the remaining blocks. Is discarding started when card is idle or right after erase command? Can it cause some other I/O requests delayed? -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
