[Deepin-Kernel-SIG] [linux 6.6.y] [Upstream] provide a sane discard_granularity default by opsiff · Pull Request #2047 · deepin-community/kernel

opsiff · 2026-08-04T10:42:27Z

Link: https://lore.kernel.org/all/20231228075545.362768-1-hch@lst.de/

Summary by Sourcery

Set a sane default discard_granularity in the block layer and rely on it instead of per-driver overrides.

New Features:

Default the global block queue discard_granularity to 512 bytes and keep it in sync with the logical block size.

Enhancements:

Ensure discard_granularity is automatically adjusted when the logical block size is increased.
Remove redundant discard_granularity settings from various block drivers to centralize discard behavior in core block code.

mainline inclusion from mainline-v6.8-rc1 category: performance A zero discard_granularity is not treated the same as a single-block one, and not having any segments after taking alignment is perfectly fine and does not need a warning. Signed-off-by: Christoph Hellwig <hch@lst.de> Link: https://lore.kernel.org/r/20231228075545.362768-2-hch@lst.de Signed-off-by: Jens Axboe <axboe@kernel.dk> (cherry picked from commit 928a5dd) Signed-off-by: Wentao Guan <guanwentao@uniontech.com>

mainline inclusion from mainline-v6.8-rc1 category: performance Just like all block I/O, discards are in units of sectors. Thus setting a smaller than sector size discard limit in case of > 512 byte sectors in bcache doesn't make sense. Always set the discard granularity to 512 bytes instead. Signed-off-by: Christoph Hellwig <hch@lst.de> Link: https://lore.kernel.org/r/20231228075545.362768-3-hch@lst.de Signed-off-by: Jens Axboe <axboe@kernel.dk> (cherry picked from commit 5e7169e) Signed-off-by: Wentao Guan <guanwentao@uniontech.com>

mainline inclusion from mainline-v6.8-rc1 category: performance Current the discard granularity defaults to 0 and must be initialized by any driver that wants to support discard. Default to the sector size instead, which is the smallest possible value, and a very useful default. Signed-off-by: Christoph Hellwig <hch@lst.de> Link: https://lore.kernel.org/r/20231228075545.362768-4-hch@lst.de Signed-off-by: Jens Axboe <axboe@kernel.dk> (cherry picked from commit 3c407dc) Signed-off-by: Wentao Guan <guanwentao@uniontech.com>

mainline inclusion from mainline-v6.8-rc1 category: performance The discard granularity now defaults to a single sector, so don't set that value explicitly. Signed-off-by: Christoph Hellwig <hch@lst.de> Acked-by: Richard Weinberger <richard@nod.at> Link: https://lore.kernel.org/r/20231228075545.362768-5-hch@lst.de Signed-off-by: Jens Axboe <axboe@kernel.dk> (cherry picked from commit 599d9d4) Signed-off-by: Wentao Guan <guanwentao@uniontech.com>

mainline inclusion from mainline-v6.8-rc1 category: performance The discard granularity now defaults to a single sector, so don't set that value explicitly. Also don't bother clearing it as a discard granularity without discard_sectors doesn't mean anything. Signed-off-by: Christoph Hellwig <hch@lst.de> Link: https://lore.kernel.org/r/20231228075545.362768-6-hch@lst.de Signed-off-by: Jens Axboe <axboe@kernel.dk> (cherry picked from commit 1e2ab2e) Signed-off-by: Wentao Guan <guanwentao@uniontech.com>

mainline inclusion from mainline-v6.8-rc1 category: performance The discard granularity now defaults to a single sector, so don't set that value explicitly. Signed-off-by: Christoph Hellwig <hch@lst.de> Link: https://lore.kernel.org/r/20231228075545.362768-7-hch@lst.de Signed-off-by: Jens Axboe <axboe@kernel.dk> (cherry picked from commit 7243254) Signed-off-by: Wentao Guan <guanwentao@uniontech.com>

mainline inclusion from mainline-v6.8-rc1 category: performance The discard granularity now defaults to a single sector, so don't set that value explicitly. Signed-off-by: Christoph Hellwig <hch@lst.de> Link: https://lore.kernel.org/r/20231228075545.362768-8-hch@lst.de Signed-off-by: Jens Axboe <axboe@kernel.dk> (cherry picked from commit 3753039) Signed-off-by: Wentao Guan <guanwentao@uniontech.com>

mainline inclusion from mainline-v6.8-rc1 category: performance The discard granularity now defaults to a single sector, so don't set that value explicitly. Signed-off-by: Christoph Hellwig <hch@lst.de> Link: https://lore.kernel.org/r/20231228075545.362768-9-hch@lst.de Signed-off-by: Jens Axboe <axboe@kernel.dk> (cherry picked from commit 105c1a5) Signed-off-by: Wentao Guan <guanwentao@uniontech.com>

mainline inclusion from mainline-v6.8-rc1 category: performance The discard granularity now defaults to a single sector, so don't set that value explicitly. Signed-off-by: Christoph Hellwig <hch@lst.de> Acked-by: Richard Weinberger <richard@nod.at> Link: https://lore.kernel.org/r/20231228075545.362768-10-hch@lst.de Signed-off-by: Jens Axboe <axboe@kernel.dk> (cherry picked from commit 31e4fac) Signed-off-by: Wentao Guan <guanwentao@uniontech.com>

sourcery-ai · 2026-08-04T10:42:33Z

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Set a sane default discard granularity in the block layer and stop individual drivers from manually poking queue->limits.discard_granularity, relying instead on core logic tied to the logical block size and default limits.

File-Level Changes

Change	Details	Files
Make discard granularity default to a sector and auto-align it with logical block size in core block queue limits.	Initialize queue_limits.discard_granularity to 512 in blk_set_default_limits instead of 0. Ensure discard_granularity is at least logical_block_size when blk_queue_logical_block_size is set. Simplify bio_split_discard by treating zero max_discard_sectors as a normal failure case without an extra comment or warning placeholder.	`block/blk-settings.c` `block/blk-merge.c`
Stop block drivers from directly setting discard_granularity and rely on block core defaults instead.	Remove explicit discard_granularity assignments in nbd setup, config teardown, and device add paths. Remove discard_granularity overrides in mtd block translation, UML ubd, null_blk, zram, and bcache device initialization when trim/discard is enabled. Retain and/or adjust max_discard_sectors configuration where appropriate so discard capability is preserved without driver-specific granularity values.	`drivers/block/nbd.c` `drivers/mtd/mtd_blkdevs.c` `arch/um/drivers/ubd_kern.c` `drivers/block/null_blk/main.c` `drivers/block/zram/zram_drv.c` `drivers/md/bcache/super.c`

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deepin-ci-robot · 2026-08-04T10:42:58Z

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
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sourcery-ai

Hey - I've left some high level feedback:

Consider replacing the hardcoded 512 in blk_set_default_limits() with a symbolic constant (e.g., SECTOR_SIZE or QUEUE_DEFAULT_SECTOR_SIZE) so the default discard granularity stays aligned with the canonical sector size definition and is easier to update globally if needed.
Now that discard_granularity is managed centrally, it may be worth adding a brief comment near blk_queue_logical_block_size() explaining the intended invariants (e.g., discard_granularity >= logical_block_size) to help future maintainers understand why drivers should not override it directly.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Consider replacing the hardcoded `512` in `blk_set_default_limits()` with a symbolic constant (e.g., `SECTOR_SIZE` or `QUEUE_DEFAULT_SECTOR_SIZE`) so the default discard granularity stays aligned with the canonical sector size definition and is easier to update globally if needed.
- Now that `discard_granularity` is managed centrally, it may be worth adding a brief comment near `blk_queue_logical_block_size()` explaining the intended invariants (e.g., `discard_granularity >= logical_block_size`) to help future maintainers understand why drivers should not override it directly.

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Copilot

Pull request overview

This PR aligns discard handling with upstream by centralizing a sane discard_granularity default in core block code (defaulting to 512 and ensuring it’s not smaller than the logical block size), and removes a set of per-driver overrides.

Changes:

Set queue_limits.discard_granularity default to 512 in blk_set_default_limits() and bump it when blk_queue_logical_block_size() increases the logical block size.
Remove driver-specific discard_granularity assignments in several block-ish drivers (mtd blktrans, bcache, zram, null_blk, nbd, ubd).
Simplify discard splitting logic in bio_split_discard().

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
drivers/mtd/mtd_blkdevs.c	Drops per-transport discard granularity override in favor of core defaults.
drivers/md/bcache/super.c	Removes hardcoded discard granularity, relying on queue defaults.
drivers/block/zram/zram_drv.c	Removes PAGE_SIZE discard granularity override.
drivers/block/null_blk/main.c	Removes redundant discard granularity assignment (now relies on core logic).
drivers/block/nbd.c	Removes explicit discard granularity set/reset, relies on core behavior.
block/blk-settings.c	Introduces default discard granularity and keeps it in sync with logical block size increases.
block/blk-merge.c	Minor simplification of discard bio splitting logic.
arch/um/drivers/ubd_kern.c	Removes explicit discard granularity assignment.

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 	blk_queue_io_min(zram->disk->queue, PAGE_SIZE);
 	blk_queue_io_opt(zram->disk->queue, PAGE_SIZE);
-	zram->disk->queue->limits.discard_granularity = PAGE_SIZE;
 	blk_queue_max_discard_sectors(zram->disk->queue, UINT_MAX);


 	blk_queue_max_discard_sectors(q, UINT_MAX);
-	q->limits.discard_granularity	= 512;
 	q->limits.io_min		= block_size;
 	q->limits.logical_block_size	= block_size;
 	q->limits.physical_block_size	= block_size;


 	lim->max_hw_discard_sectors = 0;
 	lim->max_secure_erase_sectors = 0;
-	lim->discard_granularity = 0;
+	lim->discard_granularity = 512;


Christoph Hellwig added 9 commits August 4, 2026 18:41

dongert requested a lite review from Copilot August 4, 2026 10:42

deepin-ci-robot requested a review from huangbibo August 4, 2026 10:42

Copilot started reviewing on behalf of dongert August 4, 2026 10:43 View session

sourcery-ai Bot reviewed Aug 4, 2026

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Copilot AI reviewed Aug 4, 2026

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[Deepin-Kernel-SIG] [linux 6.6.y] [Upstream] provide a sane discard_granularity default - #2047

[Deepin-Kernel-SIG] [linux 6.6.y] [Upstream] provide a sane discard_granularity default#2047
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