On 7/30/25 7:58 PM, hanqi wrote: > > ? 2025/7/30 23:20, Jens Axboe ??: >> On 7/28/25 2:28 AM, hanqi wrote: >>> ? 2025/7/28 16:07, Chao Yu ??: >>>> On 7/28/25 16:03, hanqi wrote: >>>>> ? 2025/7/28 15:38, Chao Yu ??: >>>>> >>>>>> On 7/25/25 15:53, Qi Han wrote: >>>>>>> Jens has already completed the development of uncached buffered I/O >>>>>>> in git [1], and in f2fs, uncached buffered I/O read can be enabled >>>>>>> simply by setting the FOP_DONTCACHE flag in f2fs_file_operations. >>>>>> IIUC, we may suffer lock issue when we call pwritev(.. ,RWF_DONTCACHE)? >>>>>> as Jen mentioned in below path, right? >>>>>> >>>>>> soft-irq >>>>>> - folio_end_writeback() >>>>>> - filemap_end_dropbehind_write() >>>>>> - filemap_end_dropbehind() >>>>>> - folio_unmap_invalidate() >>>>>> - lock i_lock >>>>>> >>>>>> Thanks, >>>>> That's how I understand it. >>>> So I guess we need to wait for the support RWF_DONTCACHE on write path, >>>> unless >>>> you can walk around for write path in this patch. >>>> >>>> Thanks, >>> I think the read and write paths can be submitted separately. >>> Currently, uncached buffered I/O write requires setting the >>> FGP_DONTCACHE flag when the filesystem allocates a folio. In >>> f2fs, this is done in the following path: >>> >>> - write_begin >>> - f2fs_write_begin >>> - __filemap_get_folio >>> As I understand it, if we don't set the FGP_DONTCACHE flag here, this >>> issue shouldn't occur. >> It won't cause an issue, but it also won't work in the sense that the >> intent is that if the file system doesn't support DONTCACHE, it would >> get errored at submission time. Your approach would just ignore the flag >> for writes, rather than return -EOPNOTSUPP as would be expected. >> >> You could potentially make it work just on the read side by having the >> f2fs write submit side check DONTCACHE on the write side and error them >> out. > > Hi Jens, > > Thank you for your suggestions. I am currently working on modifying > F2FS to handle the dontcache unmap operation in a workqueue. I expect > to submit the patch soon, after which F2FS should also support uncached > buffer I/O writes.
Sounds good, that's the right approach. Userspace needs to be able to rely on the fact that if RWF_DONTCACHE io is submitted without error that the target does the right thing as well, barring bugs of course. -- Jens Axboe _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
