Re: [PATCH v3 01/14] mm/zsmalloc: replace PG_private with pointer comparison

On (26/09/07 22:56), Zi Yan wrote:

zsmalloc uses PG_private to indicate first zpdesc in a zspage chain. It is
equivalent to check zpdesc == zspage->first_zpdesc. Replace
is_first_zpdesc() with zpdesc == zspage->first_zpdesc in obj_allocated().

For get_first_zpdesc(), first_zpdesc is from zspage->first_zpdesc, so
replace is_first_zpdesc() with first_zpdesc->zspage == zspage, the second
requirement of a zspage chain, where all zpdescs point to the same zspage.

is_first_zpdesc(), is only used in VM_BUG_ON_PAGE(), so performance impact
should be negligible. While at it, change VM_BUG_ON() to
VM_WARN_ON_ONCE_PAGE().

It prepares for a future commit that remove PG_private.

No functional change intended.

Assisted-by: Claude:claude-opus-4-8
Assisted-by: Codex:gpt-5
To: Minchan Kim <minchan@kernel.org>
To: Sergey Senozhatsky <senozhatsky@chromium.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Zi Yan <ziy@nvidia.com>

Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>