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Sun, 21 Dec 2025 22:42:06 -0500 X-MC-Unique: ChcZXYkiN7O8limJST5bAQ-1 X-Mimecast-MFC-AGG-ID: ChcZXYkiN7O8limJST5bAQ_1766374924 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id A2152195608D; Mon, 22 Dec 2025 03:42:02 +0000 (UTC) Received: from localhost (unknown [10.72.112.76]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 2FD561800664; Mon, 22 Dec 2025 03:41:58 +0000 (UTC) Date: Mon, 22 Dec 2025 11:41:55 +0800 From: Baoquan He To: Kairui Song Cc: linux-mm@kvack.org, Andrew Morton , Barry Song , Chris Li , Nhat Pham , Yosry Ahmed , David Hildenbrand , Johannes Weiner , Youngjun Park , Hugh Dickins , Baolin Wang , Ying Huang , Kemeng Shi , Lorenzo Stoakes , "Matthew Wilcox (Oracle)" , linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 15/19] mm, swap: add folio to swap cache directly on allocation Message-ID: References: <20251220-swap-table-p2-v5-0-8862a265a033@tencent.com> <20251220-swap-table-p2-v5-15-8862a265a033@tencent.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 On 12/22/25 at 10:42am, Kairui Song wrote: > On Sat, Dec 20, 2025 at 12:12 PM Baoquan He wrote: > > > > On 12/20/25 at 03:43am, Kairui Song wrote: > > > From: Kairui Song ...snip... > > > diff --git a/mm/swap_state.c b/mm/swap_state.c > > > index 327c051d7cd0..29fa8d313a79 100644 > > > --- a/mm/swap_state.c > > > +++ b/mm/swap_state.c > > > @@ -122,35 +122,56 @@ void *swap_cache_get_shadow(swp_entry_t entry) > > > return NULL; > > > } > > > > > > +void __swap_cache_add_folio(struct swap_cluster_info *ci, > > > + struct folio *folio, swp_entry_t entry) > > > +{ > > > + unsigned long new_tb; > > > + unsigned int ci_start, ci_off, ci_end; > > > + unsigned long nr_pages = folio_nr_pages(folio); > > > + > > > + VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio); > > > + VM_WARN_ON_ONCE_FOLIO(folio_test_swapcache(folio), folio); > > > + VM_WARN_ON_ONCE_FOLIO(!folio_test_swapbacked(folio), folio); > > > + > > > + new_tb = folio_to_swp_tb(folio); > > > + ci_start = swp_cluster_offset(entry); > > > + ci_off = ci_start; > > > + ci_end = ci_start + nr_pages; > > > + do { > > > + VM_WARN_ON_ONCE(swp_tb_is_folio(__swap_table_get(ci, ci_off))); > > > + __swap_table_set(ci, ci_off, new_tb); > > > + } while (++ci_off < ci_end); > > > + > > > + folio_ref_add(folio, nr_pages); > > > + folio_set_swapcache(folio); > > > + folio->swap = entry; > > > + > > > + node_stat_mod_folio(folio, NR_FILE_PAGES, nr_pages); > > > + lruvec_stat_mod_folio(folio, NR_SWAPCACHE, nr_pages); > > > +} > > > + > > > /** > > > * swap_cache_add_folio - Add a folio into the swap cache. > > > > With my understanding, __swap_cache_add_folio() is the pure > > functionality of adding a folio into swap cache. While > > Hi Baoquan, thanks for the review and suggestion! > > > swap_cache_add_folio() is specifically adding a folio into swap cache > > during swap in path. Not sure if we can rename them to reflect this > > clearer. At least from the functiona name and below kernel doc we can't > > feel that. Maybe: > > __swap_cache_add_folio() -> swap_cache_add_folio() > > The `__` prefix should stay, I think. This function requires the > caller to lock the swap cluster. > > > swap_cache_add_folio() -> swap_cache_add_swapin_folio() > > Indeed, my plan is that `swap_cache_add_folio` will be gone soon, we > should always call `swap_cache_alloc_folio` instead to do the swap > folio allocation in a unified way, and just remove this. > > Currently we can't do that because shmem and anon have different > routines for swapin folio allocation. Having a unified > `swap_cache_alloc_folio` will provide better swapin fallout control > and cleaner cgroup charging to avoid thrashing, etc. > > Also this helper is currently inexplicitly used by zswap writeback > too, so adding the swapin keyword seems not accurate. OK, sounds good to me. Thanks for detailed explanation.