> But could we just apply your patch only to the dsunit>=chunksize > case to fulfill your exist use case? I mean we still ignore > `dsunit` if dsunit!=chunksize and warn out users explicitly ( > `dsunit` doesn't work due to dsunit!=chunksize).
Agree. I will update patch. ________________________________________ From: Gao Xiang <hsiang...@linux.alibaba.com> Sent: Thursday, August 21, 2025 18:03 To: Su, Friendy; linux-erofs@lists.ozlabs.org Cc: Mo, Yuezhang; Palmer, Daniel (SGC) Subject: Re: [PATCH v1] erofs-utils: mkfs: Implement 'dsunit' alignment on blobdev On 2025/8/21 17: 36, Friendy. Su@ sony. com wrote: > Hi, Gao, > >> But if there is some deduplciated chunks in the logical dsunit >> boundary, don't align it at all since there is no real benefit. >> Although I'm still not On 2025/8/21 17:36, friendy...@sony.com wrote: > Hi, Gao, > >> But if there is some deduplciated chunks in the logical dsunit >> boundary, don't align it at all since there is no real benefit. >> Although I'm still not sure what's the default behavior of `dsunit` >> for chunks. > > Exactly, if `--chunksize=4096 --dsunit=512`, any 4K deduplicated will cause > PMD map failure. Can we consider the following countermeasure as default > behavior: > > 1. In man page, describe 'chunksize' and 'dsunit' should be collaborated to > achieve the best performance. Agreed, we should mention that in the manpage: > > 2. At runtime, if chunksize < dsunit, > prompt alert message, tell user it is better set chunksize=dsunit. But > still format with user set options. > The benefit is user can still set as desired. Current, for the use cases > we can imagine, chunksize=dsunit is best. But maybe users have their own use > cases, it is better let users do what they really wanted. But could we just apply your patch only to the dsunit>=chunksize case to fulfill your exist use case? I mean we still ignore `dsunit` if dsunit!=chunksize and warn out users explicitly ( `dsunit` doesn't work due to dsunit!=chunksize). I really need to think about chunksize != dsunit cases, but since you don't have such urgent need, let's keep the old `ignore` behavior for now... Thanks, Gao XIang > > > If mkfs.erofs force to align every 2M, even there is only 4K not deduplicated > in 2M, the 4K actually still occupies 2M. > 0, 2M(only 4K data new, others all deduplicated), 4M........ > Space usage efficiency is same as chunksize=dsunit=2M. > > > Best Regards > Friendy >
