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Wong" To: Joanne Koong Cc: linux-mm@kvack.org, brauner@kernel.org, willy@infradead.org, jack@suse.cz, hch@infradead.org, jlayton@kernel.org, linux-fsdevel@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH v2 12/12] iomap: add granular dirty and writeback accounting Message-ID: <20250902234604.GC1587915@frogsfrogsfrogs> References: <20250829233942.3607248-1-joannelkoong@gmail.com> <20250829233942.3607248-13-joannelkoong@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250829233942.3607248-13-joannelkoong@gmail.com> X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 9299D120003 X-Stat-Signature: ihu7z1hjfiqps7a4at4ecdcf3yaqb5w3 X-Rspam-User: X-HE-Tag: 1756856766-93289 X-HE-Meta: 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 Nni22ifo +/K+qqM4D4mc/EXGcPjU7d6CF5gtICcYucEtrNwcMWZUEUl3qToZCPdcH1VXo+qP7pafTHUTfyOfph4gh7T8hAtLhF42T6R1RxXsVb/fjizZubcGhlv2UeoWFWIbMpon+t7XSzGAOmRastZ1rjsjCRHqJss5fSRyuqy++zDMUST8AZBrQhG2vZ95SPLcUISyO7OgP+UlR7yABdD18WNYGP6ItqhaVyDaOjkfj9gcOU/PJhYcb/y58wOAStbNbKMG4A83MtsMiiRCC5PkMS4Slasse9HGEUv4mg504wEoQgaxARzFTuT0gq02NyQ== 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: On Fri, Aug 29, 2025 at 04:39:42PM -0700, Joanne Koong wrote: > Add granular dirty and writeback accounting for large folios. These > stats are used by the mm layer for dirty balancing and throttling. > Having granular dirty and writeback accounting helps prevent > over-aggressive balancing and throttling. > > There are 4 places in iomap this commit affects: > a) filemap dirtying, which now calls filemap_dirty_folio_pages() > b) writeback_iter with setting the wbc->no_stats_accounting bit and > calling clear_dirty_for_io_stats() > c) starting writeback, which now calls __folio_start_writeback() > d) ending writeback, which now calls folio_end_writeback_pages() > > This relies on using the ifs->state dirty bitmap to track dirty pages in > the folio. As such, this can only be utilized on filesystems where the > block size >= PAGE_SIZE. Er... is this statement correct? I thought that you wanted the granular dirty page accounting when it's possible that individual sub-pages of a folio could be dirty. If i_blocksize >= PAGE_SIZE, then we'll have set the min folio order and there will be exactly one (large) folio for a single fsblock. Writeback must happen in units of fsblocks, so there's no point in doing the extra accounting calculations if there's only one fsblock. Waitaminute, I think the logic to decide if you're going to use the granular accounting is: (folio_size > PAGE_SIZE && folio_size > i_blocksize) Hrm? > Signed-off-by: Joanne Koong > --- > fs/iomap/buffered-io.c | 140 ++++++++++++++++++++++++++++++++++++++--- > 1 file changed, 132 insertions(+), 8 deletions(-) > > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c > index 4f021dcaaffe..bf33a5361a39 100644 > --- a/fs/iomap/buffered-io.c > +++ b/fs/iomap/buffered-io.c > @@ -20,6 +20,8 @@ struct iomap_folio_state { > spinlock_t state_lock; > unsigned int read_bytes_pending; > atomic_t write_bytes_pending; > + /* number of pages being currently written back */ > + unsigned nr_pages_writeback; > > /* > * Each block has two bits in this bitmap: > @@ -139,6 +141,29 @@ static unsigned ifs_next_clean_block(struct folio *folio, > blks + start_blk) - blks; > } > > +static unsigned ifs_count_dirty_pages(struct folio *folio) > +{ > + struct inode *inode = folio->mapping->host; > + unsigned block_size = i_blocksize(inode); > + unsigned start_blk, end_blk; > + unsigned blks, nblks = 0; > + > + start_blk = 0; > + blks = i_blocks_per_folio(inode, folio); > + end_blk = (i_size_read(inode) - 1) >> inode->i_blkbits; > + end_blk = min(end_blk, i_blocks_per_folio(inode, folio) - 1); > + > + while (start_blk <= end_blk) { > + start_blk = ifs_next_dirty_block(folio, start_blk, end_blk); > + if (start_blk > end_blk) > + break; Use your new helper? nblks = ifs_next_clean_block(folio, start_blk + 1, end_blk) - start_blk? > + nblks++; > + start_blk++; > + } > + > + return nblks * (block_size >> PAGE_SHIFT); I think this returns the number of dirty basepages in a given large folio? If that's the case then shouldn't this return long, like folio_nr_pages does? > +} > + > static unsigned ifs_find_dirty_range(struct folio *folio, > struct iomap_folio_state *ifs, u64 *range_start, u64 range_end) > { > @@ -220,6 +245,58 @@ static void iomap_set_range_dirty(struct folio *folio, size_t off, size_t len) > ifs_set_range_dirty(folio, ifs, off, len); > } > > +static long iomap_get_range_newly_dirtied(struct folio *folio, loff_t pos, > + unsigned len) iomap_count_clean_pages() ? --D > +{ > + struct inode *inode = folio->mapping->host; > + unsigned block_size = i_blocksize(inode); > + unsigned start_blk, end_blk; > + unsigned nblks = 0; > + > + start_blk = pos >> inode->i_blkbits; > + end_blk = (pos + len - 1) >> inode->i_blkbits; > + end_blk = min(end_blk, i_blocks_per_folio(inode, folio) - 1); > + > + while (start_blk <= end_blk) { > + /* count how many clean blocks there are */ > + start_blk = ifs_next_clean_block(folio, start_blk, end_blk); > + if (start_blk > end_blk) > + break; > + nblks++; > + start_blk++; > + } > + > + return nblks * (block_size >> PAGE_SHIFT); > +} > + > +static bool iomap_granular_dirty_pages(struct folio *folio) > +{ > + struct iomap_folio_state *ifs = folio->private; > + > + if (!ifs) > + return false; > + > + return i_blocksize(folio->mapping->host) >= PAGE_SIZE; > +} > + > +static bool iomap_dirty_folio_range(struct address_space *mapping, > + struct folio *folio, loff_t pos, unsigned len) > +{ > + long nr_new_dirty_pages; > + > + if (!iomap_granular_dirty_pages(folio)) { > + iomap_set_range_dirty(folio, pos, len); > + return filemap_dirty_folio(mapping, folio); > + } > + > + nr_new_dirty_pages = iomap_get_range_newly_dirtied(folio, pos, len); > + if (!nr_new_dirty_pages) > + return false; > + > + iomap_set_range_dirty(folio, pos, len); > + return filemap_dirty_folio_pages(mapping, folio, nr_new_dirty_pages); > +} > + > static struct iomap_folio_state *ifs_alloc(struct inode *inode, > struct folio *folio, unsigned int flags) > { > @@ -712,8 +789,7 @@ bool iomap_dirty_folio(struct address_space *mapping, struct folio *folio) > size_t len = folio_size(folio); > > ifs_alloc(inode, folio, 0); > - iomap_set_range_dirty(folio, 0, len); > - return filemap_dirty_folio(mapping, folio); > + return iomap_dirty_folio_range(mapping, folio, 0, len); > } > EXPORT_SYMBOL_GPL(iomap_dirty_folio); > > @@ -937,8 +1013,8 @@ static bool __iomap_write_end(struct inode *inode, loff_t pos, size_t len, > if (unlikely(copied < len && !folio_test_uptodate(folio))) > return false; > iomap_set_range_uptodate(folio, offset_in_folio(folio, pos), len); > - iomap_set_range_dirty(folio, offset_in_folio(folio, pos), copied); > - filemap_dirty_folio(inode->i_mapping, folio); > + iomap_dirty_folio_range(inode->i_mapping, folio, > + offset_in_folio(folio, pos), copied); > return true; > } > > @@ -1613,6 +1689,29 @@ void iomap_start_folio_write(struct inode *inode, struct folio *folio, > } > EXPORT_SYMBOL_GPL(iomap_start_folio_write); > > +static void iomap_folio_start_writeback(struct folio *folio) > +{ > + struct iomap_folio_state *ifs = folio->private; > + > + if (!iomap_granular_dirty_pages(folio)) > + return folio_start_writeback(folio); > + > + __folio_start_writeback(folio, false, ifs->nr_pages_writeback); > +} > + > +static void iomap_folio_end_writeback(struct folio *folio) > +{ > + struct iomap_folio_state *ifs = folio->private; > + long nr_pages_writeback; > + > + if (!iomap_granular_dirty_pages(folio)) > + return folio_end_writeback(folio); > + > + nr_pages_writeback = ifs->nr_pages_writeback; > + ifs->nr_pages_writeback = 0; > + folio_end_writeback_pages(folio, nr_pages_writeback); > +} > + > void iomap_finish_folio_write(struct inode *inode, struct folio *folio, > size_t len) > { > @@ -1622,7 +1721,7 @@ void iomap_finish_folio_write(struct inode *inode, struct folio *folio, > WARN_ON_ONCE(ifs && atomic_read(&ifs->write_bytes_pending) <= 0); > > if (!ifs || atomic_sub_and_test(len, &ifs->write_bytes_pending)) > - folio_end_writeback(folio); > + iomap_folio_end_writeback(folio); > } > EXPORT_SYMBOL_GPL(iomap_finish_folio_write); > > @@ -1710,6 +1809,21 @@ static bool iomap_writeback_handle_eof(struct folio *folio, struct inode *inode, > return true; > } > > +static void iomap_update_dirty_stats(struct folio *folio) > +{ > + struct iomap_folio_state *ifs = folio->private; > + long nr_dirty_pages; > + > + if (iomap_granular_dirty_pages(folio)) { > + nr_dirty_pages = ifs_count_dirty_pages(folio); > + ifs->nr_pages_writeback = nr_dirty_pages; > + } else { > + nr_dirty_pages = folio_nr_pages(folio); > + } > + > + clear_dirty_for_io_stats(folio, nr_dirty_pages); > +} > + > int iomap_writeback_folio(struct iomap_writepage_ctx *wpc, struct folio *folio) > { > struct iomap_folio_state *ifs = folio->private; > @@ -1727,6 +1841,8 @@ int iomap_writeback_folio(struct iomap_writepage_ctx *wpc, struct folio *folio) > > trace_iomap_writeback_folio(inode, pos, folio_size(folio)); > > + iomap_update_dirty_stats(folio); > + > if (!iomap_writeback_handle_eof(folio, inode, &end_pos)) > return 0; > WARN_ON_ONCE(end_pos <= pos); > @@ -1734,6 +1850,7 @@ int iomap_writeback_folio(struct iomap_writepage_ctx *wpc, struct folio *folio) > if (i_blocks_per_folio(inode, folio) > 1) { > if (!ifs) { > ifs = ifs_alloc(inode, folio, 0); > + ifs->nr_pages_writeback = folio_nr_pages(folio); > iomap_set_range_dirty(folio, 0, end_pos - pos); > } > > @@ -1751,7 +1868,7 @@ int iomap_writeback_folio(struct iomap_writepage_ctx *wpc, struct folio *folio) > * Set the writeback bit ASAP, as the I/O completion for the single > * block per folio case happen hit as soon as we're submitting the bio. > */ > - folio_start_writeback(folio); > + iomap_folio_start_writeback(folio); > > /* > * Walk through the folio to find dirty areas to write back. > @@ -1784,10 +1901,10 @@ int iomap_writeback_folio(struct iomap_writepage_ctx *wpc, struct folio *folio) > */ > if (ifs) { > if (atomic_dec_and_test(&ifs->write_bytes_pending)) > - folio_end_writeback(folio); > + iomap_folio_end_writeback(folio); > } else { > if (!wb_pending) > - folio_end_writeback(folio); > + iomap_folio_end_writeback(folio); > } > mapping_set_error(inode->i_mapping, error); > return error; > @@ -1809,6 +1926,13 @@ iomap_writepages(struct iomap_writepage_ctx *wpc) > PF_MEMALLOC)) > return -EIO; > > + /* > + * iomap opts out of the default wbc stats accounting because it does > + * its own granular dirty/writeback accounting (see > + * iomap_update_dirty_stats()). > + */ > + wpc->wbc->no_stats_accounting = true; > + > while ((folio = writeback_iter(mapping, wpc->wbc, folio, &error))) { > error = iomap_writeback_folio(wpc, folio); > folio_unlock(folio); > -- > 2.47.3 > >