On Wed, Aug 15, 2018 at 06:20:16PM +0200, Marek Vasut wrote: > On 08/15/2018 06:12 PM, Tom Rini wrote: > > On Wed, Aug 15, 2018 at 06:04:50PM +0200, Marek Vasut wrote: > > > >> On 08/15/2018 04:30 PM, Tom Rini wrote: > >>> On Wed, Aug 08, 2018 at 01:20:29PM +0200, Marek Vasut wrote: > >>> > >>>> Cache up to 4 kiB entries. 4 kiB is the default block size on ext4, yet > >>>> the underlying block layer devices usually report support for 512B . In > >>>> most cases, the 512B support is emulated (ie. SD cards, SSDs, USB sticks > >>>> etc.) and the real block size of those devices is much bigger. > >>>> > >>>> To avoid performance degradation with such devices and FS setup, bump > >>>> the maximum cache entry size to 4 kiB. > >>>> > >>>> Signed-off-by: Marek Vasut <[email protected]> > >>>> Cc: Tom Rini <[email protected]> > >>>> Cc: Simon Glass <[email protected]> > >>> > >>> Reviewed-by: Tom Rini <[email protected]> > >>> > >>> I'll pick this up post v2018.09 if no one objects, thanks! > >> > >> I object. I was hoping there'd be some discussion on how to solve this > >> in a future-proof manner ... it's only a matter of time until someone > >> uses ext4 with 8k blocks on an SSD ... > > > > In general, sure? In specific, mkfs.ext4 1.42.13 man page says 1/2/4KiB > > are the only valid values of block size, and based on having to whack > > this for some other projects it's pretty common for OpenEmbedded at > > least to spit out 1KiB block size images. > > OE spits 4k , that's how I triggered it, > meta/classes/image_types.bbclass:EXTRA_IMAGECMD_ext2 ?= "-i 4096" > meta/classes/image_types.bbclass:EXTRA_IMAGECMD_ext3 ?= "-i 4096" > meta/classes/image_types.bbclass:EXTRA_IMAGECMD_ext4 ?= "-i 4096"
That's bytes-per-inode, I was referring to block size which is -b and dynamic unless specified. > > So unless you know of cases > > today (or tomorrow, but not next year) where 8KiB is common or likely, > > we should probably just bump this for now and maybe make it a tunable so > > it's easily changed? > > It is already tunable, see blkcache config in blkcache command. > > But what I'd like to see is somehow the FS and the underlying storage > negotiating the best settings. Can we get the FS block size from the > block cache perspective ? Good questions that I don't have an answer to. -- Tom
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