Re: [PATCH 2/4] mtd: rfd_ftl: add discard support

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hi Sean,

Sean Young <sean@mess.org> wrote on Sat, 7 Aug 2021 09:06:33 +0100:

> On Fri, Aug 06, 2021 at 08:18:20PM +0200, Miquel Raynal wrote:
> > Hi Sean,
> > 
> > Sean Young <sean@mess.org> wrote on Tue, 13 Jul 2021 10:44:01 +0100:
> >   
> > > I proposed this change 16 years ago before discard was a feature in
> > > the block layer: https://lwn.net/Articles/162776/
> > > 
> > > Now that the block layer has discard, we can finally merge this change.  
> > 
> > Can you explain why this is needed here?  
> 
> Because discard is a huge win. This is also known as trim.
> 
> By implementing discard, both fstrim and the discard filesystem option
> can be used.
> 
> Implementing discard in the ftl means that when files are removed, there
> is less data in the ftl mapping. This means less stuff to move around for
> erasing and also less erasing to do. This means better wear levelling.

And this is a good commit message for v2 :-)

> 
> There is also a wikipedia page on trim here:
> 
> 	https://en.wikipedia.org/wiki/Trim_(computing)

Got it, thanks!

> 
> Thanks,
> 
> Sean
> 
> > (also please add the maintainers in Cc: for the v2)
> >   
> > > Signed-off-by: Sean Young <sean@mess.org>
> > > ---
> > >  drivers/mtd/rfd_ftl.c | 29 +++++++++++++++++++++++++++++
> > >  1 file changed, 29 insertions(+)
> > > 
> > > diff --git a/drivers/mtd/rfd_ftl.c b/drivers/mtd/rfd_ftl.c
> > > index 7b243f2b2fa3..7f5f6d247cae 100644
> > > --- a/drivers/mtd/rfd_ftl.c
> > > +++ b/drivers/mtd/rfd_ftl.c
> > > @@ -705,6 +705,34 @@ static int rfd_ftl_writesect(struct mtd_blktrans_dev *dev, u_long sector, char *
> > >  	return rc;
> > >  }
> > >  
> > > +static int rfd_ftl_discardsect(struct mtd_blktrans_dev *dev,
> > > +			       unsigned long sector, unsigned int nr_sects)
> > > +{
> > > +	struct partition *part = (struct partition *)dev;
> > > +	u_long addr;
> > > +	int rc;
> > > +
> > > +	while (nr_sects) {
> > > +		if (sector >= part->sector_count)
> > > +			return -EIO;
> > > +
> > > +		addr = part->sector_map[sector];
> > > +
> > > +		if (addr != -1) {
> > > +			rc = mark_sector_deleted(part, addr);
> > > +			if (rc)
> > > +				return rc;
> > > +
> > > +			part->sector_map[sector] = -1;
> > > +		}
> > > +
> > > +		sector++;
> > > +		nr_sects--;
> > > +	}
> > > +
> > > +	return 0;
> > > +}
> > > +
> > >  static int rfd_ftl_getgeo(struct mtd_blktrans_dev *dev, struct hd_geometry *geo)
> > >  {
> > >  	struct partition *part = (struct partition*)dev;
> > > @@ -786,6 +814,7 @@ static struct mtd_blktrans_ops rfd_ftl_tr = {
> > >  
> > >  	.readsect	= rfd_ftl_readsect,
> > >  	.writesect	= rfd_ftl_writesect,
> > > +	.discard	= rfd_ftl_discardsect,
> > >  	.getgeo		= rfd_ftl_getgeo,
> > >  	.add_mtd	= rfd_ftl_add_mtd,
> > >  	.remove_dev	= rfd_ftl_remove_dev,  
> > 
> > 
> > 
> > 
> > Thanks,
> > Miquèl
> > 
> > ______________________________________________________
> > Linux MTD discussion mailing list
> > http://lists.infradead.org/mailman/listinfo/linux-mtd/  




Thanks,
Miquèl

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