mm: reinstate unconditional writeback start in balance_dirty_pages()#934
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vfsci-bot[bot] wants to merge 1 commit intovfs.base.cifrom
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mm: reinstate unconditional writeback start in balance_dirty_pages()#934vfsci-bot[bot] wants to merge 1 commit intovfs.base.cifrom
vfsci-bot[bot] wants to merge 1 commit intovfs.base.cifrom
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Commit 64dd89a ("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. Fixes: 64dd89a ("mm/block/fs: remove laptop_mode") Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
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Series: https://patchwork.kernel.org/project/linux-fsdevel/list/?series=1073196
Submitter: Joanne Koong
Version: 2
Patches: 1/1
Message-ID:
<20260326215127.3857682-1-joannelkoong@gmail.com>Base: vfs.base.ci
Lore: https://lore.kernel.org/linux-fsdevel/20260326215127.3857682-1-joannelkoong@gmail.com
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