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Wed, 17 Dec 2025 22:37:36 -0500 X-MC-Unique: 4gkqZ1yrM2if8ZS1n76vxQ-1 X-Mimecast-MFC-AGG-ID: 4gkqZ1yrM2if8ZS1n76vxQ_1766029053 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (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-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 50FE91955F34; Thu, 18 Dec 2025 03:37:33 +0000 (UTC) Received: from localhost (unknown [10.72.112.95]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id EBD6E30001A2; Thu, 18 Dec 2025 03:37:30 +0000 (UTC) Date: Thu, 18 Dec 2025 11:37:25 +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, Kairui Song Subject: Re: [PATCH v4 13/19] mm, swap: remove workaround for unsynchronized swap map cache state Message-ID: References: <20251205-swap-table-p2-v4-0-cb7e28a26a40@tencent.com> <20251205-swap-table-p2-v4-13-cb7e28a26a40@tencent.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251205-swap-table-p2-v4-13-cb7e28a26a40@tencent.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 X-Rspam-User: X-Rspamd-Queue-Id: 24EFE40002 X-Rspamd-Server: rspam04 X-Stat-Signature: paotsm9yzzkmym31kjnu3cipix6sby9a X-HE-Tag: 1766029059-83581 X-HE-Meta: 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 LmAxqWWV ECKLqr9XnOqxJPjPwbUak03H6LO09mKnESTybxQw80Om1by9ChsyLSHiSRTdq1+Ghxyr9k1ukJkPI80T/EcOVYL+u1bl4A6VrjIW1Ok0EVX4M/Prnf9SkzT2SDIZ9+gTu8OwAYgeWsQedwBLhqIXI11SWLE9GK9Jm/aJvewC0MaMoXQP0CMnCSut6+Zg8RaCysTkEKi1IDplK7tCtop7KmpwFrK+HLy/YPbAu08iEjA3z6Jqy/AN50noBEDIASDje5sWVYMggwJ6UBKkUIbm6wElpEGsyGPRh/VyyyaW4zs/jp2gNPsscVI3YucllDSAfu2bA6Fz1QY2cThI1iYY+ABOjd0wrvK5hTbiNxqKppf0TNBfQdhCMEknB34xdukVUWijKzad9j/S488ByqqgQDYkISj/aDAXTyRgqYEFM0yakQEVYs+DPGzJc2QwTDaRn6vcM X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 12/05/25 at 03:29am, Kairui Song wrote: > From: Kairui Song > > Remove the "skip if exists" check from commit a65b0e7607ccb ("zswap: > make shrinking memcg-aware"). It was needed because there is a tiny time > window between setting the SWAP_HAS_CACHE bit and actually adding the > folio to the swap cache. If a user is trying to add the folio into the > swap cache but another user was interrupted after setting SWAP_HAS_CACHE > but hasn't added the folio to the swap cache yet, it might lead to a > deadlock. > > We have moved the bit setting to the same critical section as adding the > folio, so this is no longer needed. Remove it and clean it up. > > Signed-off-by: Kairui Song > --- > mm/swap.h | 2 +- > mm/swap_state.c | 27 ++++++++++----------------- > mm/zswap.c | 2 +- > 3 files changed, 12 insertions(+), 19 deletions(-) Reviewed-by: Baoquan He > > diff --git a/mm/swap.h b/mm/swap.h > index b5075a1aee04..6777b2ab9d92 100644 > --- a/mm/swap.h > +++ b/mm/swap.h > @@ -260,7 +260,7 @@ int swap_cache_add_folio(struct folio *folio, swp_entry_t entry, > void swap_cache_del_folio(struct folio *folio); > struct folio *swap_cache_alloc_folio(swp_entry_t entry, gfp_t gfp_flags, > struct mempolicy *mpol, pgoff_t ilx, > - bool *alloced, bool skip_if_exists); > + bool *alloced); > /* Below helpers require the caller to lock and pass in the swap cluster. */ > void __swap_cache_del_folio(struct swap_cluster_info *ci, > struct folio *folio, swp_entry_t entry, void *shadow); > diff --git a/mm/swap_state.c b/mm/swap_state.c > index df7df8b75e52..1a69ba3be87f 100644 > --- a/mm/swap_state.c > +++ b/mm/swap_state.c > @@ -445,8 +445,6 @@ void swap_update_readahead(struct folio *folio, struct vm_area_struct *vma, > * @folio: folio to be added. > * @gfp: memory allocation flags for charge, can be 0 if @charged if true. > * @charged: if the folio is already charged. > - * @skip_if_exists: if the slot is in a cached state, return NULL. > - * This is an old workaround that will be removed shortly. > * > * Update the swap_map and add folio as swap cache, typically before swapin. > * All swap slots covered by the folio must have a non-zero swap count. > @@ -457,8 +455,7 @@ void swap_update_readahead(struct folio *folio, struct vm_area_struct *vma, > */ > static struct folio *__swap_cache_prepare_and_add(swp_entry_t entry, > struct folio *folio, > - gfp_t gfp, bool charged, > - bool skip_if_exists) > + gfp_t gfp, bool charged) > { > struct folio *swapcache = NULL; > void *shadow; > @@ -478,7 +475,7 @@ static struct folio *__swap_cache_prepare_and_add(swp_entry_t entry, > * might return a folio that is irrelevant to the faulting > * entry because @entry is aligned down. Just return NULL. > */ > - if (ret != -EEXIST || skip_if_exists || folio_test_large(folio)) > + if (ret != -EEXIST || folio_test_large(folio)) > goto failed; > > swapcache = swap_cache_get_folio(entry); > @@ -511,8 +508,6 @@ static struct folio *__swap_cache_prepare_and_add(swp_entry_t entry, > * @mpol: NUMA memory allocation policy to be applied > * @ilx: NUMA interleave index, for use only when MPOL_INTERLEAVE > * @new_page_allocated: sets true if allocation happened, false otherwise > - * @skip_if_exists: if the slot is a partially cached state, return NULL. > - * This is a workaround that would be removed shortly. > * > * Allocate a folio in the swap cache for one swap slot, typically before > * doing IO (e.g. swap in or zswap writeback). The swap slot indicated by > @@ -525,8 +520,7 @@ static struct folio *__swap_cache_prepare_and_add(swp_entry_t entry, > */ > struct folio *swap_cache_alloc_folio(swp_entry_t entry, gfp_t gfp_mask, > struct mempolicy *mpol, pgoff_t ilx, > - bool *new_page_allocated, > - bool skip_if_exists) > + bool *new_page_allocated) > { > struct swap_info_struct *si = __swap_entry_to_info(entry); > struct folio *folio; > @@ -547,8 +541,7 @@ struct folio *swap_cache_alloc_folio(swp_entry_t entry, gfp_t gfp_mask, > if (!folio) > return NULL; > /* Try add the new folio, returns existing folio or NULL on failure. */ > - result = __swap_cache_prepare_and_add(entry, folio, gfp_mask, > - false, skip_if_exists); > + result = __swap_cache_prepare_and_add(entry, folio, gfp_mask, false); > if (result == folio) > *new_page_allocated = true; > else > @@ -577,7 +570,7 @@ struct folio *swapin_folio(swp_entry_t entry, struct folio *folio) > unsigned long nr_pages = folio_nr_pages(folio); > > entry = swp_entry(swp_type(entry), round_down(offset, nr_pages)); > - swapcache = __swap_cache_prepare_and_add(entry, folio, 0, true, false); > + swapcache = __swap_cache_prepare_and_add(entry, folio, 0, true); > if (swapcache == folio) > swap_read_folio(folio, NULL); > return swapcache; > @@ -605,7 +598,7 @@ struct folio *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, > > mpol = get_vma_policy(vma, addr, 0, &ilx); > folio = swap_cache_alloc_folio(entry, gfp_mask, mpol, ilx, > - &page_allocated, false); > + &page_allocated); > mpol_cond_put(mpol); > > if (page_allocated) > @@ -724,7 +717,7 @@ struct folio *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask, > /* Ok, do the async read-ahead now */ > folio = swap_cache_alloc_folio( > swp_entry(swp_type(entry), offset), gfp_mask, mpol, ilx, > - &page_allocated, false); > + &page_allocated); > if (!folio) > continue; > if (page_allocated) { > @@ -742,7 +735,7 @@ struct folio *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask, > skip: > /* The page was likely read above, so no need for plugging here */ > folio = swap_cache_alloc_folio(entry, gfp_mask, mpol, ilx, > - &page_allocated, false); > + &page_allocated); > if (unlikely(page_allocated)) > swap_read_folio(folio, NULL); > return folio; > @@ -847,7 +840,7 @@ static struct folio *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask, > continue; > } > folio = swap_cache_alloc_folio(entry, gfp_mask, mpol, ilx, > - &page_allocated, false); > + &page_allocated); > if (si) > put_swap_device(si); > if (!folio) > @@ -869,7 +862,7 @@ static struct folio *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask, > skip: > /* The folio was likely read above, so no need for plugging here */ > folio = swap_cache_alloc_folio(targ_entry, gfp_mask, mpol, targ_ilx, > - &page_allocated, false); > + &page_allocated); > if (unlikely(page_allocated)) > swap_read_folio(folio, NULL); > return folio; > diff --git a/mm/zswap.c b/mm/zswap.c > index a7a2443912f4..d8a33db9d3cc 100644 > --- a/mm/zswap.c > +++ b/mm/zswap.c > @@ -1015,7 +1015,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry, > > mpol = get_task_policy(current); > folio = swap_cache_alloc_folio(swpentry, GFP_KERNEL, mpol, > - NO_INTERLEAVE_INDEX, &folio_was_allocated, true); > + NO_INTERLEAVE_INDEX, &folio_was_allocated); > put_swap_device(si); > if (!folio) > return -ENOMEM; > > -- > 2.52.0 >