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Date: Tue, 03 Jul 2012 13:47:31 +0200 From: Paolo Bonzini <pbonzini@...hat.com> To: Vivek Goyal <vgoyal@...hat.com> CC: linux-kernel@...r.kernel.org, axboe@...nel.dk, snitzer@...hat.com, martin.petersen@...cle.com, david@...morbit.com, xfs@....sgi.com, dm-devel@...hat.com, hch@....de Subject: Re: [dm-devel] [PATCH v2 2/3] block: reorganize rounding of max_discard_sectors Il 03/07/2012 04:49, Vivek Goyal ha scritto: >> > + /* Zero-sector (unknown) and one-sector granularities are the same. */ >> > + granularity = max(q->limits.discard_granularity >> 9, 1U); >> > + >> > /* >> > * Ensure that max_discard_sectors is of the proper >> > * granularity >> > */ >> > max_discard_sectors = min(q->limits.max_discard_sectors, UINT_MAX >> 9); >> > + max_discard_sectors = round_down(max_discard_sectors, granularity); >> > if (unlikely(!max_discard_sectors)) { >> > /* Avoid infinite loop below. Being cautious never hurts. */ >> > return -EOPNOTSUPP; >> > - } else if (q->limits.discard_granularity) { >> > - unsigned int disc_sects = q->limits.discard_granularity >> 9; >> > - >> > - max_discard_sectors &= ~(disc_sects - 1); > This is kind of odd. If discard_granularity is zero, we assume that > discards are supported and granularity is 1. But if max_discard_sectors > is zero, we assume discards are disabled. Not sure if we should treat > max_discard_sectors and discard_granularity in same way or not. Yes, this keeps the same behavior as before. It is also the one that is consistent with drivers/scsi/sd.c. sd_config_discard always sets limits.discard_granularity and then uses limits.max_discard_sectors to disable discards. Paolo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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