On 10/30, Eric Biggers wrote:
> On Wed, Oct 30, 2019 at 04:43:52PM +0800, Chao Yu wrote:
> > On 2019/10/30 10:55, Eric Biggers wrote:
> > > On Tue, Oct 29, 2019 at 04:33:36PM +0800, Chao Yu wrote:
> > >> On 2019/10/28 6:50, Eric Biggers wrote:
> > >>>> +bool f2fs_is_compressed_page(struct page *page)
> > >>>> +{
> > >>>> + if (!page_private(page))
> > >>>> + return false;
> > >>>> + if (IS_ATOMIC_WRITTEN_PAGE(page) || IS_DUMMY_WRITTEN_PAGE(page))
> > >>>> + return false;
> > >>>> + return *((u32 *)page_private(page)) ==
> > >>>> F2FS_COMPRESSED_PAGE_MAGIC;
> > >>>> +}
> > >>>
> > >>> This code implies that there can be multiple page private structures
> > >>> each of
> > >>> which has a different magic number. But I only see
> > >>> F2FS_COMPRESSED_PAGE_MAGIC.
> > >>> Where in the code is the other one(s)?
> > >>
> > >> I'm not sure I understood you correctly, did you mean it needs to
> > >> introduce
> > >> f2fs_is_atomic_written_page() and f2fs_is_dummy_written_page() like
> > >> f2fs_is_compressed_page()?
> > >>
> > >
> > > No, I'm asking what is the case where the line
> > >
> > > *((u32 *)page_private(page)) == F2FS_COMPRESSED_PAGE_MAGIC
> > >
> > > returns false?
> >
> > Should be this?
> >
> > if (!page_private(page))
> > return false;
> > f2fs_bug_on(*((u32 *)page_private(page)) != F2FS_COMPRESSED_PAGE_MAGIC)
> > return true;
>
> Yes, that makes more sense, unless there are other cases.
>
> >
> > >
> > >>>
> > >>>> +
> > >>>> +static void f2fs_set_compressed_page(struct page *page,
> > >>>> + struct inode *inode, pgoff_t index, void *data,
> > >>>> refcount_t *r)
> > >>>> +{
> > >>>> + SetPagePrivate(page);
> > >>>> + set_page_private(page, (unsigned long)data);
> > >>>> +
> > >>>> + /* i_crypto_info and iv index */
> > >>>> + page->index = index;
> > >>>> + page->mapping = inode->i_mapping;
> > >>>> + if (r)
> > >>>> + refcount_inc(r);
> > >>>> +}
> > >>>
> > >>> It isn't really appropriate to create fake pagecache pages like this.
> > >>> Did you
> > >>> consider changing f2fs to use fscrypt_decrypt_block_inplace() instead?
> > >>
> > >> We need to store i_crypto_info and iv index somewhere, in order to pass
> > >> them to
> > >> fscrypt_decrypt_block_inplace(), where did you suggest to store them?
> > >>
> > >
> > > The same place where the pages are stored.
> >
> > Still we need allocate space for those fields, any strong reason to do so?
> >
>
> page->mapping set implies that the page is a pagecache page. Faking it could
> cause problems with code elsewhere.
I've checked it with minchan, and it seems to be fine that filesystem uses
this page internally only, not in pagecache.
>
> > >
> > >>>> +
> > >>>> +void f2fs_destroy_compress_ctx(struct compress_ctx *cc)
> > >>>> +{
> > >>>> + kvfree(cc->rpages);
> > >>>> +}
> > >>>
> > >>> The memory is allocated with kzalloc(), so why is it freed with
> > >>> kvfree() and not
> > >>> just kfree()?
> > >>
> > >> It was allocated by f2fs_*alloc() which will fallback to kvmalloc() once
> > >> kmalloc() failed.
> > >
> > > This seems to be a bug in f2fs_kmalloc() -- it inappropriately falls back
> > > to
> > > kvmalloc(). As per its name, it should only use kmalloc().
> > > f2fs_kvmalloc()
> > > already exists, so it can be used when the fallback is wanted.
> >
> > We can introduce f2fs_memalloc() to wrap f2fs_kmalloc() and f2fs_kvmalloc()
> > as
> > below:
> >
> > f2fs_memalloc()
> > {
> > mem = f2fs_kmalloc();
> > if (mem)
> > return mem;
> > return f2fs_kvmalloc();
> > }
> >
> > It can be used in specified place where we really need it, like the place
> > descirbied in 5222595d093e ("f2fs: use kvmalloc, if kmalloc is failed") in
> > where
> > we introduced original logic.
>
> No, just use kvmalloc(). The whole point of kvmalloc() is that it tries
> kmalloc() and then falls back to vmalloc() if it fails.
>
> - Eric
_______________________________________________
Linux-f2fs-devel mailing list
Linux-f2fs-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
