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d=pankajraghav.com; s=MBO0001; t=1715788797; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=SCQ5EwlnBaVjjGBU3qX9WnT4s0ilKb0cfBcFSyoSM6k=; b=t/rLh24W0RY6M4EoaSW/hUED3I3C6M87G+4uVJfnfbFTkkFszL2pKyCJqCbwdytSw5Ze1m Q5dhksBxEbN4R6uRkpzlg5IX+Y4p85aSf0clO8MyulvvYL/71VC5gyC8H86cb/0aDZGZaz K2des+IBCFa3WPHGm/BP1yMvJgcru8EDx2cvVhPZ12AEvJiuWk0wUq8R9UurxmcsHCX5RH vZz3O8OLvoB1QKhzETWlTv2I+jYJHhoT59qEq5Xly2fLyITn8dtxOC+0+4yyTMDWPMVm7f J+hGeREPyQ5bOXxlPwFpvQhwamx/qZAX173rWmCV1wdVJnZ4e0xmBTDMK/Fx5w== Date: Wed, 15 May 2024 15:59:43 +0000 From: "Pankaj Raghav (Samsung)" To: Matthew Wilcox , david@fromorbit.com, djwong@kernel.org, hch@lst.de Cc: Keith Busch , mcgrof@kernel.org, akpm@linux-foundation.org, brauner@kernel.org, chandan.babu@oracle.com, gost.dev@samsung.com, hare@suse.de, john.g.garry@oracle.com, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-xfs@vger.kernel.org, p.raghav@samsung.com, ritesh.list@gmail.com, ziy@nvidia.com Subject: Re: [RFC] iomap: use huge zero folio in iomap_dio_zero Message-ID: <20240515155943.2uaa23nvddmgtkul@quentin> References: <20240503095353.3798063-8-mcgrof@kernel.org> <20240507145811.52987-1-kernel@pankajraghav.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: C447AC002A X-Stat-Signature: a8zh7tq51fahjwre4q31py89pua7dgwt X-HE-Tag: 1715788802-679757 X-HE-Meta: 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 cHxSCyfq ricKjBGyGUKPo45xo3n7un62hsg0J4SJbLfAs1bkZ0Y4iY9gadNkttXbrkg9zJnPuprJFzFeKW6Mhj/p+R2IIcyGAc0ksCmYztbdn7L4ASZyWClPr5qNMa6pQlOUtd24P9q09SygsM6QNIqThvaBtYRM/WmMU4Wg/X8udOtt3/9LFE/BoVFRpUbCFoZirAOSMBZTc5Z4R+eVI3on68QmdtqOb4glU4OArJwj0HNev3HLBViu3khV8auoVjF4RPum+UnEeVBuinOQz/GlaGCKXH5ShXWl9fLYf+BFUMVeFUnFTEDQ/dutGGNAbhV/vpyij9Z1O X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > so unless submit_bio() can handle the fallback to "create a new bio > full of zeroes and resubmit it to the device" if the original fails, > we're a little mismatched. I'm not really familiar with either part of > this code, so I don't have much in the way of bright ideas. Perhaps > we go back to the "allocate a large folio at filesystem mount" plan. So one thing that became clear after yesterday's discussion was to **not** use a PMD page for sub block zeroing as in some architectures we will be using a lot of memory (such as ARM) to zero out a 64k FS block. So Chinner proposed the idea of using iomap_init function to alloc large zero folio that could be used in iomap_dio_zero(). The general agreement was 64k large folio is enough for now. We could always increase it and optimize it in the future when required. This is a rough prototype of what it might look like: diff --git a/fs/internal.h b/fs/internal.h index 7ca738904e34..dad5734b2f75 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -35,6 +35,12 @@ static inline void bdev_cache_init(void) int __block_write_begin_int(struct folio *folio, loff_t pos, unsigned len, get_block_t *get_block, const struct iomap *iomap); +/* + * iomap/buffered-io.c + */ + +extern struct folio *zero_fsb_folio; + /* * char_dev.c */ diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c index 4e8e41c8b3c0..48235765df7a 100644 --- a/fs/iomap/buffered-io.c +++ b/fs/iomap/buffered-io.c @@ -42,6 +42,7 @@ struct iomap_folio_state { }; static struct bio_set iomap_ioend_bioset; +struct folio *zero_fsb_folio; static inline bool ifs_is_fully_uptodate(struct folio *folio, struct iomap_folio_state *ifs) @@ -1985,8 +1986,15 @@ iomap_writepages(struct address_space *mapping, struct writeback_control *wbc, } EXPORT_SYMBOL_GPL(iomap_writepages); + static int __init iomap_init(void) { + void *addr = kzalloc(16 * PAGE_SIZE, GFP_KERNEL); + + if (!addr) + return -ENOMEM; + + zero_fsb_folio = virt_to_folio(addr); return bioset_init(&iomap_ioend_bioset, 4 * (PAGE_SIZE / SECTOR_SIZE), offsetof(struct iomap_ioend, io_bio), BIOSET_NEED_BVECS); diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c index f3b43d223a46..59a65c3ccf13 100644 --- a/fs/iomap/direct-io.c +++ b/fs/iomap/direct-io.c @@ -236,17 +236,23 @@ static void iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio, loff_t pos, unsigned len) { struct inode *inode = file_inode(dio->iocb->ki_filp); - struct page *page = ZERO_PAGE(0); struct bio *bio; - bio = iomap_dio_alloc_bio(iter, dio, 1, REQ_OP_WRITE | REQ_SYNC | REQ_IDLE); + /* + * The zero folio used is 64k. + */ + WARN_ON_ONCE(len > (16 * PAGE_SIZE)); + + bio = iomap_dio_alloc_bio(iter, dio, BIO_MAX_VECS, + REQ_OP_WRITE | REQ_SYNC | REQ_IDLE); fscrypt_set_bio_crypt_ctx(bio, inode, pos >> inode->i_blkbits, GFP_KERNEL); + bio->bi_iter.bi_sector = iomap_sector(&iter->iomap, pos); bio->bi_private = dio; bio->bi_end_io = iomap_dio_bio_end_io; - __bio_add_page(bio, page, len, 0); + bio_add_folio_nofail(bio, zero_fsb_folio, len, 0); iomap_dio_submit_bio(iter, dio, bio, pos); }