Hi, On 6/29/23 11:28, Sumitra Sharma wrote: > On Wed, Jun 28, 2023 at 06:15:04PM +0100, Matthew Wilcox wrote: >> Here's a more comprehensive read_folio patch. It's not at all >> efficient, but then if we wanted an efficient vboxsf, we'd implement >> vboxsf_readahead() and actually do an async call with deferred setting >> of the uptodate flag. I can consult with anyone who wants to do all >> this work. >> >> I haven't even compiled this, just trying to show the direction this >> should take. >> >> diff --git a/fs/vboxsf/file.c b/fs/vboxsf/file.c >> index 2307f8037efc..f1af9a7bd3d8 100644 >> --- a/fs/vboxsf/file.c >> +++ b/fs/vboxsf/file.c >> @@ -227,26 +227,31 @@ const struct inode_operations vboxsf_reg_iops = { >> >> static int vboxsf_read_folio(struct file *file, struct folio *folio) >> { >> - struct page *page = &folio->page; >> struct vboxsf_handle *sf_handle = file->private_data; >> - loff_t off = page_offset(page); >> - u32 nread = PAGE_SIZE; >> - u8 *buf; >> + loff_t pos = folio_pos(folio); >> + size_t offset = 0; >> int err; >> >> - buf = kmap(page); >> + do { >> + u8 *buf = kmap_local_folio(folio, offset); >> + u32 nread = PAGE_SIZE; >> >> - err = vboxsf_read(sf_handle->root, sf_handle->handle, off, &nread, buf); >> - if (err == 0) { >> - memset(&buf[nread], 0, PAGE_SIZE - nread); >> - flush_dcache_page(page); >> - SetPageUptodate(page); >> - } else { >> - SetPageError(page); >> - } >> + err = vboxsf_read(sf_handle->root, sf_handle->handle, pos, >> + &nread, buf); >> + if (nread < PAGE_SIZE) >> + memset(&buf[nread], 0, PAGE_SIZE - nread); >> + kunmap_local(buf); >> + if (err) >> + break; >> + offset += PAGE_SIZE; >> + pos += PAGE_SIZE; >> + } while (offset < folio_size(folio); >> >> - kunmap(page); >> - unlock_page(page); >> + if (!err) { >> + flush_dcache_folio(folio); >> + folio_mark_uptodate(folio); >> + } >> + folio_unlock(folio); >> return err; >> } >> > > Hi > > So, after reading the comments, I understood that the problem presented > by Hans and Matthew is as follows: > > 1) In the current code, the buffers used by vboxsf_write()/vboxsf_read() are > translated to PAGELIST-s before passing to the hypervisor, > but inefficiently— it first maps a page in vboxsf_read_folio() and then > calls page_to_phys(virt_to_page()) in the function hgcm_call_init_linaddr(). > > The inefficiency in the current implementation arises due to the unnecessary > mapping of a page in vboxsf_read_folio() because the mapping output, i.e. the > linear address, is used deep down in file 'drivers/virt/vboxguest/vboxguest_utils.c'. > Hence, the mapping must be done in this file; to do so, the folio must be passed > until this point. It can be done by adding a new member, 'struct folio *folio', > in the 'struct vmmdev_hgcm_function_parameter64'. struct vmmdev_hgcm_function_parameter64 is defined in include/uapi/linux/vbox_vmmdev_types.h This is part of the userspace API of vboxguest which allows userspace to make (some) VirtualBox hypervisor request through a chardev. You can not just go and change this struct. Note there already is a VMMDEV_HGCM_PARM_TYPE_PAGELIST type. So you could do the conversion from folio to pagelist (see the vboxguest code for how to do this) in the vboxsf_read() code (making it take a folio pointer as arg) and then directly pass the pagelist to the vbg_hgcm_call(). > The unused member 'phys_addr' in this struct can also be removed. Again no you can NOT just go and make changes to an uapi header. Regards, Hans