Messages in this thread | | | Date | Wed, 30 Oct 2019 09:50:56 -0700 | From | Eric Biggers <> | Subject | Re: [PATCH 2/2] f2fs: support data compression |
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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.
> > > >>>> + > >>>> +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
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