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b=jApyfLSGiPS84kYB+liZcP1w29V8W514VORp+A4UcSvyS/iAQfrLBszs7g9P9qOCV ytH2FXO3V/7w+sfVM3aloQgb7EGzbmmvB67bcaTEEf5XfxuxMMvcJ1oSJC0QnvWxoL ws29x8lMfdhpzaKbKCC7GlrTR800w7yUMURB6BUDqIW+KeVuKjrmT04HLzPK7lLNqt pckImXTFhuL+QJTur40oNyPqljxzH7cU4zOHAChFQkOuTLLyR+YP1XJ1ZyO4xNJtA5 DPwxwemSUnnc+K813/P0Cm3c73gF+JSuNu9WyQVjfEFK2jJ1oygAQ1XCeUAF7rXCj6 kODTzJ5Cw8OGg== Date: Fri, 23 Oct 2026 15:22:09 +0100 From: Harry Yoo To: Qing Wang Cc: Vlastimil Babka , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/slab: only require the requested size when refilling prefilled sheaves Message-ID: References: <20261023094401.2042862-1-wangqing7171@gmail.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261023094401.2042862-1-wangqing7171@gmail.com> X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: EA5511C0005 X-Stat-Signature: 5owkosgggpimwyazfsr5k8cufrmmocnc X-Rspam-User: X-Spam-Status: No, score=-11.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1792765332-587357 X-HE-Meta: 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 hh0GmisJ xxGo3+H3wRZ34UJhN6pKjoDp90B6FZQOLHn4ZziyysN5SE5D+U77xM8QJn0uTTll3LF1intlSUe+QxfRSjNckRikk6YZXbpPNrbGtkm/zNMnOa1mQpoR1P1Wd5qmE28o6+MogwbcBuW24gQrKQbqPe5jBYFUe6e3W4gbeLihcBtWYH5GAeoBo9/ON/IRWVnD53JpocepIunvJmGvP0Jy78TyvGnsWUNHdV5v0y5qJUGHptoB8Fu6AXIn1NlTmRsMby52QRVqbVsIG0HbM6MMzQmm7/Q== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Fri, Oct 23, 2026 at 05:44:01PM +0800, Qing Wang wrote: > kmem_cache_prefill_sheaf() and kmem_cache_refill_sheaf() only guarantee > @size objects, but for standard capacity sheaves > __prefill_sheaf_pfmemalloc() uses refill_sheaf(), which actually fills > the sheaf up to s->sheaf_capacity. > > The call thus fails with -ENOMEM > whenever the sheaf cannot be filled > completely, even when @size objects were already obtained. This is extremely rare condition to happen, and so... > This leads to needless flushing of the partially > filled sheaf in kmem_cache_prefill_sheaf(), It doesn't make much sense to micro-optimize slab in low or out of memory situations. > and may use pfmemalloc > reserves to fill the sheaf beyond what was requested. But the request size itself is a speculation and unused objects will be returned back to the allocator anyway. > Pass the @size from kmem_cache_prefill_sheaf() and > kmem_cache_refill_sheaf() down to __prefill_sheaf_pfmemalloc(), and have > it use the newly added refill_sheaf_min(), which returns success once > the sheaf holds @min_size objects while still trying to fill it up to > s->sheaf_capacity. > > refill_sheaf() remains the full-capacity variant for > __pcs_replace_empty_main() and kmem_cache_return_sheaf(), because sheaves > on the barn's full list must be full. > > Signed-off-by: Qing Wang -- Cheers, Harry / Hyeonggon