Hi Eric, (add some mm folks...)
On Wed, Oct 30, 2019 at 09:50:56AM -0700, Eric Biggers wrote: <snip> > > >>> > > >>> 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. Not very related with this patch. Faking page->mapping was used in zsmalloc before nonLRU migration (see material [1]) and use in erofs now (page->mapping to indicate nonLRU short lifetime temporary page type, page->private is used for per-page information), as far as I know, NonLRU page without PAGE_MAPPING_MOVABLE set is safe for most mm code. On the other hands, I think NULL page->mapping will waste such field in precious page structure... And we can not get such page type directly only by a NULL -- a truncated file page or just allocated page or some type internal temporary pages... So I have some proposal is to use page->mapping to indicate specific page type for such nonLRU pages (by some common convention, e.g. some real structure, rather than just zero out to waste 8 bytes, it's also natural to indicate some page type by its `mapping' naming )... Since my English is not very well, I delay it util now... [1] https://elixir.bootlin.com/linux/v3.18.140/source/mm/zsmalloc.c#L379 https://lore.kernel.org/linux-mm/1459321935-3655-7-git-send-email-minc...@kernel.org and some not very related topic: https://lwn.net/Articles/752564/ Thanks, Gao Xiang _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
