On Monday 28 March 2011, Kyungmin Park wrote: > So you will go through (blocks, bytes...) 0 -> 20 > > OOOO==O===OO===OOOOO==O===O===OOOOOOO=== > ^ ^ > 0 20 > > So, you will call discard on extents: > > 0-3 > You'll skip 6 because is smaller than minlen > 10-11 > 15-19 > > instead of > > 0-3 > 10-11 > 15-19 > 30-36 Sorry for joining the discussion late, but shouldn't you also pass the alignment of the discards? FAT is typically used on cheap media that have very limited support for garbage-collection, such as eMMC or SD cards. On most SDHC cards, you only ever want to issue discard on full erase blocks (allocation units per spec), typically sized 4 MB. If you just pass the minimum length, the file system could end up erasing a 4 MB section that spans two half erase blocks, or it could span a few clusters of the following erase block, both of which is not desirable from a performance point of view. On other media, you have the same problem inside an erase block: These might be able to discard parts of an erase block efficiently, but normally not less than a flash page (typically 8 to 32 KB). Again, you don't want to discard partial pages in this case, and that is much more important than discarding a large number of pages because it would result in an immediate copy-on-write operation. Further, when you erase some pages inside of an erase block, you probably should not span multiple erase blocks but instead issue separate requests for each set of pages in one erase block. Arnd Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
