On Tue, Mar 16, 2021 at 8:00 PM chenjun (AM) <chenjun102@xxxxxxxxxx> wrote: > > 在 2021/3/12 1:25, Dan Williams 写道: > > On Thu, Mar 11, 2021 at 4:20 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > >> > >> On Thu, Mar 11, 2021 at 07:48:25AM +0000, chenjun (AM) wrote: > >>> static int dax_writeback_one(struct xa_state *xas, struct dax_device > >>> *dax_dev, struct address_space *mapping, void *entry) > >>> ----dax_flush(dax_dev, page_address(pfn_to_page(pfn)), count * PAGE_SIZE); > >>> The pfn is returned by the driver. In my case, the pfn does not have > >>> struct page. so pfn_to_page(pfn) return a wrong address. > >> > >> I wasn't involved, but I think the right solution here is simply to > >> replace page_address(pfn_to_page(pfn)) with pfn_to_virt(pfn). I don't > >> know why Dan decided to do this in the more complicated way. > > > > pfn_to_virt() only works for the direct-map. If pages are not mapped I > > don't see how pfn_to_virt() is expected to work. > > > > The real question Chenjun is why are you writing a new simulator of > > memory as a block-device vs reusing the pmem driver or brd? > > > > Hi Dan > > In my case, I do not want to take memory to create the struct page of > the memory my driver used. There are efforts happening to drastically reduce that overhead. You might want to check out Joao's work [1]. I think that direction holds more promise than trying to extend FS_DAX_LIMITED. [1]: http://lore.kernel.org/r/20201208172901.17384-1-joao.m.martins@xxxxxxxxxx > And, I think this is also a problem for DCSSBLK. If I understand correctly DAX replaced XIP for S390. There have not been reports about this problem, and I can only guess because XIP (eXecute-In-Place) is a read-only use case where dax_writeback_one() is never triggered, or S390 just isn't using DCSSBLK anymore. The last time I touched FS_DAX_LIMITED the DCSSBLK maintainers offered to just delete this driver to get it out of the way. > > So I want to go back the older way if CONFIG_FS_DAX_LIMITED > > diff --git a/fs/dax.c b/fs/dax.c > index b3d27fd..6395e84 100644 > --- a/fs/dax.c > +++ b/fs/dax.c > @@ -867,6 +867,9 @@ static int dax_writeback_one(struct xa_state *xas, > struct dax_device *dax_dev, > { > unsigned long pfn, index, count; > long ret = 0; > + void *kaddr; > + pfn_t new_pfn_t; > + pgoff_t pgoff; > > /* > * A page got tagged dirty in DAX mapping? Something is seriously > @@ -926,7 +929,25 @@ static int dax_writeback_one(struct xa_state *xas, > struct dax_device *dax_dev, > index = xas->xa_index & ~(count - 1); > > dax_entry_mkclean(mapping, index, pfn); > - dax_flush(dax_dev, page_address(pfn_to_page(pfn)), count * PAGE_SIZE); > + > + if (!IS_ENABLED(CONFIG_FS_DAX_LIMITED) || pfn_valid(pfn)) > + kaddr = page_address(pfn_to_page(pfn)); > + else { > + ret = bdev_dax_pgoff(mapping->host->i_sb->s_bdev, pfn << > PFN_SECTION_SHIFT, count << PAGE_SHIFT, &pgoff); This is broken: mapping->host->i_sb->s_bdev ...there is no guarantee that the superblock associated with the mapping is hosted on the same block device associated with the passed in dax_device. See dax_rtdev in xfs_open_devices().
