Re: [PATCH v5] mm/page_alloc: only update lowmem_reserve_ratio on sysctl write

[Vlastimil Babka (SUSE)]

On 8/6/26 10:27, Jianlin Shi wrote:
> lowmem_reserve_ratio_sysctl_handler() ignores the return value of
> proc_dointvec_minmax() and always calls setup_per_zone_lowmem_reserve(),
> even for read operations.
> 
> Fix three issues:
> 
> 1. Propagate errors from proc_dointvec_minmax() instead of always
>    returning success.  For example, writing non-integer garbage to the
>    sysctl now returns an error instead of silently succeeding with
>    unchanged values.
> 
> 2. Only call setup_per_zone_lowmem_reserve() when the sysctl is
>    actually written, matching the write-only refresh pattern of
>    min_free_kbytes and watermark_scale_factor handlers.
> 
> 3. On write, parse into a temporary ratio[] array and only copy into
>    sysctl_lowmem_reserve_ratio[] and refresh derived state after the
>    full vector is validated.  This avoids leaving the ratio array
>    partially updated while skipping setup when proc_dointvec_minmax()
>    returns an error on a later element (suggested by Andrew Morton).
> 
> Drop the manual "< 1 -> 0" sanitization loop and set .extra1 =
> SYSCTL_ZERO on the ctl_table entry so proc_dointvec_minmax() enforces
> the minimum on write; negative values now return -EINVAL instead of
> being silently coerced to 0 (suggested by Vlastimil Babka).
> 
> Link: https://lore.kernel.org/linux-mm/tencent_FFD4F4D728AAE8A8AE0AF277A59854A29A06@xxxxxx/
> 
> Signed-off-by: Jianlin Shi <shijianlin11@xxxxxxxxxxx>

Acked-by: Vlastimil Babka (SUSE) <vbabka@xxxxxxxxxx>