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Commit64dd89ae01("mm/block/fs: remove laptop_mode") removed this unconditional writeback start from balance_dirty_pages(): if (unlikely(!writeback_in_progress(wb))) wb_start_background_writeback(wb); This logic needs to be reinstated to prevent performance regressions for strictlimited BDIs and memcg setups. The problem occurs because: a) For strictlimited BDIs, throttling is calculated using per-wb thresholds. The per-wb threshold can be exceeded even when the global dirty threshold was not exceeded (nr_dirty < gdtc->bg_thresh) b) For memcg-based throttling, memcg uses its own dirty count / thresholds and can trigger throttling even when the global threshold isn't exceeded Without the unconditional writeback start, IO is throttled as it waits for dirty pages to be written back but there is no writeback running. This leads to severe stalls. On fuse, buffered write performance dropped from 1400 MiB/s to 2000 KiB/s. Reinstate the unconditional writeback start so that writeback is guaranteed to be running whenever IO needs to be throttled. Link: https://lkml.kernel.org/r/20260326215127.3857682-2-joannelkoong@gmail.com Fixes:64dd89ae01("mm/block/fs: remove laptop_mode") Signed-off-by: Joanne Koong <joannelkoong@gmail.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. 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