From: Baolin Wang <baolin.wang@linux.alibaba.com>
To: Hungyu Lin <dennylin0707@gmail.com>, hughd@google.com
Cc: akpm@linux-foundation.org, tim.c.chen@linux.intel.com,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] shmem: clamp negative used-block samples in statfs
Date: Wed, 28 Oct 2026 14:58:20 +0800 [thread overview]
Message-ID: <bb3b1c3d-f656-4238-9c89-2639687b6f8e@linux.alibaba.com> (raw)
In-Reply-To: <20261028051826.23058-1-dennylin0707@gmail.com>
On 10/28/26 1:18 PM, Hungyu Lin wrote:
> percpu_counter_sum() holds the counter lock while scanning the per-CPU
> values, but local updates can still proceed. Concurrent allocation and
> freeing on different CPUs can therefore produce a negative sample even
> though the number of used tmpfs blocks cannot be negative.
>
> shmem_statfs() subtracts this sample from max_blocks, reporting more free
> blocks than the filesystem's total. With a one-page file being written
> and truncated on separate CPUs, GNU df reports negative used space, for
> example 67108864 total bytes, -28672 used and 67137536 available.
>
> Use percpu_counter_sum_positive() to clamp a negative sample to zero.
> This keeps the existing best-effort accounting in statfs and does not
> change allocation or limit enforcement.
>
> Fixes: 7e496299d4d2 ("tmpfs: make tmpfs scalable with percpu_counter for used blocks")
> Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>
> Signed-off-by: Hungyu Lin <dennylin0707@gmail.com>
> ---
LGTM.
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
prev parent reply other threads:[~2026-10-28 6:58 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-28 5:18 Hungyu Lin
2026-10-28 6:58 ` Baolin Wang [this message]
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