From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-124.freemail.mail.aliyun.com (out30-124.freemail.mail.aliyun.com [115.124.30.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 67EADB67E for ; Fri, 2 Aug 2024 02:10:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722564604; cv=none; b=s4MbtP5/Dy3AX1ccAr93VjJeQXBxujtpHsWKP7BlkHCbL2Cb0syR6HrSFf7kXDYTh9FI7xFDOsHTM9+XGQ8df9mrd9zWDADCujPuR20IyTXX/UxH6S3Wta6f8J3YfP2EY7MgGdkRIYobAMLbXvXgl3rLStw2mI2KtM3Efr/6zvI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722564604; c=relaxed/simple; bh=76dudD5b6Lb3j6PBOVkzeU/2fGT22Qcl2jOeZZqA3x8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ElldLvM8pkgIPJmvGV1p1Py3LvOhbExyHqqt+qQ48InAlxGCutGfvLet1iAfgxmU24scaLBj3Jjo+YLk5NyFtCL03RLMxQZ0gASDZWei4bjl+i7LO5cfj9Me2tFWbsxaIRJgFnkMKlXjqhdbwnVBYN8Dv+xOBFoQoviOiamQGYY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=OUShvBSY; arc=none smtp.client-ip=115.124.30.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="OUShvBSY" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1722564599; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=gLurZOJ2zskorg7UXJtTXMjc16vqpy3IgxaglNm6Wwo=; b=OUShvBSYxPNzhIl/z+Dow1bLjWhVBXgP1KNQqNDcCyOfEC6BLAwIpoxDhKsmBxNOZU0qSsJmYn1Z78TaMQ1/V9jgvFjUJlI6s+Skv8DX8BlLIyaW33dqJZiJQgWJumro5fiFbFOZNjbo578qcSl7x8ls5gAbAeDeKZTrB9Hy60Q= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R191e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033037067109;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=23;SR=0;TI=SMTPD_---0WBvZjmz_1722564595; Received: from 30.97.56.76(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0WBvZjmz_1722564595) by smtp.aliyun-inc.com; Fri, 02 Aug 2024 10:09:57 +0800 Message-ID: Date: Fri, 2 Aug 2024 10:09:55 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/1] mm: swap: add nr argument in swapcache_prepare and swapcache_clear to support large folios To: Barry Song <21cnbao@gmail.com>, ying.huang@intel.com Cc: akpm@linux-foundation.org, chrisl@kernel.org, david@redhat.com, hannes@cmpxchg.org, hughd@google.com, kaleshsingh@google.com, kasong@tencent.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mhocko@suse.com, minchan@kernel.org, nphamcs@gmail.com, ryan.roberts@arm.com, senozhatsky@chromium.org, shakeel.butt@linux.dev, shy828301@gmail.com, surenb@google.com, v-songbaohua@oppo.com, willy@infradead.org, xiang@kernel.org, yosryahmed@google.com References: <87sevpj6xp.fsf@yhuang6-desk2.ccr.corp.intel.com> <20240801092014.41549-1-21cnbao@gmail.com> From: Baolin Wang In-Reply-To: <20240801092014.41549-1-21cnbao@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2024/8/1 17:20, Barry Song wrote: > On Thu, Aug 1, 2024 at 2:50 PM Huang, Ying wrote: >> >> Barry Song <21cnbao@gmail.com> writes: >> >>> On Thu, Aug 1, 2024 at 10:37 AM Huang, Ying wrote: >>>> >>>> Barry Song <21cnbao@gmail.com> writes: >>>> >>>>> On Thu, Aug 1, 2024 at 9:13 AM Huang, Ying wrote: >>>>>> >>>>>> Barry Song <21cnbao@gmail.com> writes: >>>>>> >>>>>>> On Wed, Jul 31, 2024 at 4:28 PM Huang, Ying wrote: >>>>>>>> >>>>>>>> Barry Song <21cnbao@gmail.com> writes: >>>>>>>> >>>>>>>>> On Wed, Jul 31, 2024 at 4:14 PM Huang, Ying wrote: >>>>>>>>>> >>>>>>>>>> Hi, Barry, >>>>>>>>>> >>>>>>>>>> Barry Song <21cnbao@gmail.com> writes: >>>>>>>>>> >>>>>>>>>>> From: Barry Song >>>>>>>>>>> >>>>>>>>>>> Right now, swapcache_prepare() and swapcache_clear() supports one entry >>>>>>>>>>> only, to support large folios, we need to handle multiple swap entries. >>>>>>>>>>> >>>>>>>>>>> To optimize stack usage, we iterate twice in __swap_duplicate(): the >>>>>>>>>>> first time to verify that all entries are valid, and the second time >>>>>>>>>>> to apply the modifications to the entries. >>>>>>>>>>> >>>>>>>>>>> Currently, we're using nr=1 for the existing users. >>>>>>>>>>> >>>>>>>>>>> Reviewed-by: Baolin Wang >>>>>>>>>>> Signed-off-by: Barry Song >>>>>>>>>>> --- >>>>>>>>>>>  include/linux/swap.h |   4 +- >>>>>>>>>>>  mm/memory.c          |   6 +-- >>>>>>>>>>>  mm/swap.h            |   5 ++- >>>>>>>>>>>  mm/swap_state.c      |   2 +- >>>>>>>>>>>  mm/swapfile.c        | 101 +++++++++++++++++++++++++------------------ >>>>>>>>>>>  5 files changed, 68 insertions(+), 50 deletions(-) >>>>>>>>>>> >>>>>>>>>>> diff --git a/include/linux/swap.h b/include/linux/swap.h >>>>>>>>>>> index ba7ea95d1c57..5b920fa2315b 100644 >>>>>>>>>>> --- a/include/linux/swap.h >>>>>>>>>>> +++ b/include/linux/swap.h >>>>>>>>>>> @@ -480,7 +480,7 @@ extern int get_swap_pages(int n, swp_entry_t swp_entries[], int order); >>>>>>>>>>>  extern int add_swap_count_continuation(swp_entry_t, gfp_t); >>>>>>>>>>>  extern void swap_shmem_alloc(swp_entry_t); >>>>>>>>>>>  extern int swap_duplicate(swp_entry_t); >>>>>>>>>>> -extern int swapcache_prepare(swp_entry_t); >>>>>>>>>>> +extern int swapcache_prepare(swp_entry_t entry, int nr); >>>>>>>>>>>  extern void swap_free_nr(swp_entry_t entry, int nr_pages); >>>>>>>>>>>  extern void swapcache_free_entries(swp_entry_t *entries, int n); >>>>>>>>>>>  extern void free_swap_and_cache_nr(swp_entry_t entry, int nr); >>>>>>>>>>> @@ -554,7 +554,7 @@ static inline int swap_duplicate(swp_entry_t swp) >>>>>>>>>>>       return 0; >>>>>>>>>>>  } >>>>>>>>>>> >>>>>>>>>>> -static inline int swapcache_prepare(swp_entry_t swp) >>>>>>>>>>> +static inline int swapcache_prepare(swp_entry_t swp, int nr) >>>>>>>>>>>  { >>>>>>>>>>>       return 0; >>>>>>>>>>>  } >>>>>>>>>>> diff --git a/mm/memory.c b/mm/memory.c >>>>>>>>>>> index 833d2cad6eb2..b8675617a5e3 100644 >>>>>>>>>>> --- a/mm/memory.c >>>>>>>>>>> +++ b/mm/memory.c >>>>>>>>>>> @@ -4081,7 +4081,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) >>>>>>>>>>>                        * reusing the same entry. It's undetectable as >>>>>>>>>>>                        * pte_same() returns true due to entry reuse. >>>>>>>>>>>                        */ >>>>>>>>>>> -                     if (swapcache_prepare(entry)) { >>>>>>>>>>> +                     if (swapcache_prepare(entry, 1)) { >>>>>>>>>>>                               /* Relax a bit to prevent rapid repeated page faults */ >>>>>>>>>>>                               schedule_timeout_uninterruptible(1); >>>>>>>>>>>                               goto out; >>>>>>>>>>> @@ -4387,7 +4387,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) >>>>>>>>>>>  out: >>>>>>>>>>>       /* Clear the swap cache pin for direct swapin after PTL unlock */ >>>>>>>>>>>       if (need_clear_cache) >>>>>>>>>>> -             swapcache_clear(si, entry); >>>>>>>>>>> +             swapcache_clear(si, entry, 1); >>>>>>>>>>>       if (si) >>>>>>>>>>>               put_swap_device(si); >>>>>>>>>>>       return ret; >>>>>>>>>>> @@ -4403,7 +4403,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) >>>>>>>>>>>               folio_put(swapcache); >>>>>>>>>>>       } >>>>>>>>>>>       if (need_clear_cache) >>>>>>>>>>> -             swapcache_clear(si, entry); >>>>>>>>>>> +             swapcache_clear(si, entry, 1); >>>>>>>>>>>       if (si) >>>>>>>>>>>               put_swap_device(si); >>>>>>>>>>>       return ret; >>>>>>>>>>> diff --git a/mm/swap.h b/mm/swap.h >>>>>>>>>>> index baa1fa946b34..7c6330561d84 100644 >>>>>>>>>>> --- a/mm/swap.h >>>>>>>>>>> +++ b/mm/swap.h >>>>>>>>>>> @@ -59,7 +59,7 @@ void __delete_from_swap_cache(struct folio *folio, >>>>>>>>>>>  void delete_from_swap_cache(struct folio *folio); >>>>>>>>>>>  void clear_shadow_from_swap_cache(int type, unsigned long begin, >>>>>>>>>>>                                 unsigned long end); >>>>>>>>>>> -void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry); >>>>>>>>>>> +void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry, int nr); >>>>>>>>>>>  struct folio *swap_cache_get_folio(swp_entry_t entry, >>>>>>>>>>>               struct vm_area_struct *vma, unsigned long addr); >>>>>>>>>>>  struct folio *filemap_get_incore_folio(struct address_space *mapping, >>>>>>>>>>> @@ -120,7 +120,7 @@ static inline int swap_writepage(struct page *p, struct writeback_control *wbc) >>>>>>>>>>>       return 0; >>>>>>>>>>>  } >>>>>>>>>>> >>>>>>>>>>> -static inline void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry) >>>>>>>>>>> +static inline void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry, int nr) >>>>>>>>>>>  { >>>>>>>>>>>  } >>>>>>>>>>> >>>>>>>>>>> @@ -172,4 +172,5 @@ static inline unsigned int folio_swap_flags(struct folio *folio) >>>>>>>>>>>       return 0; >>>>>>>>>>>  } >>>>>>>>>>>  #endif /* CONFIG_SWAP */ >>>>>>>>>>> + >>>>>>>>>> >>>>>>>>>> NITPICK: Is it necessary to add a blank line here?  But I don't think a >>>>>>>>>> new version is necessary if this is the only change needed. >>>>>>>>> >>>>>>>>> No need to add a blank line; it was probably a mistake I made in Vim. >>>>>>>>> >>>>>>>>>> >>>>>>>>>>>  #endif /* _MM_SWAP_H */ >>>>>>>>>>> diff --git a/mm/swap_state.c b/mm/swap_state.c >>>>>>>>>>> index a1726e49a5eb..b06f2a054f5a 100644 >>>>>>>>>>> --- a/mm/swap_state.c >>>>>>>>>>> +++ b/mm/swap_state.c >>>>>>>>>>> @@ -477,7 +477,7 @@ struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, >>>>>>>>>>>               /* >>>>>>>>>>>                * Swap entry may have been freed since our caller observed it. >>>>>>>>>>>                */ >>>>>>>>>>> -             err = swapcache_prepare(entry); >>>>>>>>>>> +             err = swapcache_prepare(entry, 1); >>>>>>>>>>>               if (!err) >>>>>>>>>>>                       break; >>>>>>>>>>> >>>>>>>>>>> diff --git a/mm/swapfile.c b/mm/swapfile.c >>>>>>>>>>> index 5f73a8553371..757d38a86f56 100644 >>>>>>>>>>> --- a/mm/swapfile.c >>>>>>>>>>> +++ b/mm/swapfile.c >>>>>>>>>>> @@ -3363,7 +3363,7 @@ void si_swapinfo(struct sysinfo *val) >>>>>>>>>>>  } >>>>>>>>>>> >>>>>>>>>>>  /* >>>>>>>>>>> - * Verify that a swap entry is valid and increment its swap map count. >>>>>>>>>>> + * Verify that nr swap entries are valid and increment their swap map counts. >>>>>>>>>>>   * >>>>>>>>>>>   * Returns error code in following case. >>>>>>>>>>>   * - success -> 0 >>>>>>>>>>> @@ -3373,60 +3373,77 @@ void si_swapinfo(struct sysinfo *val) >>>>>>>>>>>   * - swap-cache reference is requested but the entry is not used. -> ENOENT >>>>>>>>>>>   * - swap-mapped reference requested but needs continued swap count. -> ENOMEM >>>>>>>>>>>   */ >>>>>>>>>>> -static int __swap_duplicate(swp_entry_t entry, unsigned char usage) >>>>>>>>>>> +static int __swap_duplicate(swp_entry_t entry, unsigned char usage, int nr) >>>>>>>>>>>  { >>>>>>>>>>>       struct swap_info_struct *p; >>>>>>>>>>>       struct swap_cluster_info *ci; >>>>>>>>>>>       unsigned long offset; >>>>>>>>>>>       unsigned char count; >>>>>>>>>>>       unsigned char has_cache; >>>>>>>>>>> -     int err; >>>>>>>>>>> +     int err, i; >>>>>>>>>>> >>>>>>>>>>>       p = swp_swap_info(entry); >>>>>>>>>>> >>>>>>>>>>>       offset = swp_offset(entry); >>>>>>>>>>> +     VM_WARN_ON(nr > SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER); >>>>>>>>>>>       ci = lock_cluster_or_swap_info(p, offset); >>>>>>>>>>> >>>>>>>>>>> -     count = p->swap_map[offset]; >>>>>>>>>>> +     err = 0; >>>>>>>>>>> +     for (i = 0; i < nr; i++) { >>>>>>>>>>> +             count = p->swap_map[offset + i]; >>>>>>>>>>> >>>>>>>>>>> -     /* >>>>>>>>>>> -      * swapin_readahead() doesn't check if a swap entry is valid, so the >>>>>>>>>>> -      * swap entry could be SWAP_MAP_BAD. Check here with lock held. >>>>>>>>>>> -      */ >>>>>>>>>>> -     if (unlikely(swap_count(count) == SWAP_MAP_BAD)) { >>>>>>>>>>> -             err = -ENOENT; >>>>>>>>>>> -             goto unlock_out; >>>>>>>>>>> -     } >>>>>>>>>>> +             /* >>>>>>>>>>> +              * swapin_readahead() doesn't check if a swap entry is valid, so the >>>>>>>>>>> +              * swap entry could be SWAP_MAP_BAD. Check here with lock held. >>>>>>>>>>> +              */ >>>>>>>>>>> +             if (unlikely(swap_count(count) == SWAP_MAP_BAD)) { >>>>>>>>>>> +                     err = -ENOENT; >>>>>>>>>>> +                     goto unlock_out; >>>>>>>>>>> +             } >>>>>>>>>>> >>>>>>>>>>> -     has_cache = count & SWAP_HAS_CACHE; >>>>>>>>>>> -     count &= ~SWAP_HAS_CACHE; >>>>>>>>>>> -     err = 0; >>>>>>>>>>> +             has_cache = count & SWAP_HAS_CACHE; >>>>>>>>>>> +             count &= ~SWAP_HAS_CACHE; >>>>>>>>>>> >>>>>>>>>>> -     if (usage == SWAP_HAS_CACHE) { >>>>>>>>>>> +             if (usage == SWAP_HAS_CACHE) { >>>>>>>>>>> +                     /* set SWAP_HAS_CACHE if there is no cache and entry is used */ >>>>>>>>>>> +                     if (!has_cache && count) >>>>>>>>>>> +                             continue; >>>>>>>>>>> +                     else if (has_cache)             /* someone else added cache */ >>>>>>>>>>> +                             err = -EEXIST; >>>>>>>>>>> +                     else                            /* no users remaining */ >>>>>>>>>>> +                             err = -ENOENT; >>>>>>>>>>> >>>>>>>>>>> -             /* set SWAP_HAS_CACHE if there is no cache and entry is used */ >>>>>>>>>>> -             if (!has_cache && count) >>>>>>>>>>> -                     has_cache = SWAP_HAS_CACHE; >>>>>>>>>>> -             else if (has_cache)             /* someone else added cache */ >>>>>>>>>>> -                     err = -EEXIST; >>>>>>>>>>> -             else                            /* no users remaining */ >>>>>>>>>>> -                     err = -ENOENT; >>>>>>>>>>> +             } else if (count || has_cache) { >>>>>>>>>>> >>>>>>>>>>> -     } else if (count || has_cache) { >>>>>>>>>>> +                     if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX) >>>>>>>>>>> +                             continue; >>>>>>>>>>> +                     else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX) >>>>>>>>>>> +                             err = -EINVAL; >>>>>>>>>>> +                     else if (swap_count_continued(p, offset + i, count)) >>>>>>>>>>> +                             continue; >>>>>>>>>> >>>>>>>>>> IIUC, this will make the change to swap map directly instead of >>>>>>>>>> verification.  If the verification failed for some entry later, the >>>>>>>>>> count will be wrong?  Or I missed something? >>>>>>>>> >>>>>>>>> To avoid using a bitmap or a larger stack, we actually verify during >>>>>>>>> the first iteration. >>>>>>>>> This ensures that by the second iteration, we can safely commit the >>>>>>>>> modification. >>>>>>>>> >>>>>>>>> I actually put some words in the changelog :-) >>>>>>>>> >>>>>>>>> To optimize stack usage, we iterate twice in __swap_duplicate(): the >>>>>>>>> first time to verify that all entries are valid, and the second time >>>>>>>>> to apply the modifications to the entries. >>>>>>>> >>>>>>>> Yes, I have seen it and I think that it is a good strategy. >>>>>>>> >>>>>>>> But, IIUC, swap_count_continued() will change the higher bits of the >>>>>>>> swap_map instead of verifying.  Or, my understanding is wrong? >>>>>>>> >>>>>>> >>>>>>> Ying, your understanding is 100% correct. but the code also has nothing >>>>>>> broken. we didn't extend swap_duplicate() to have argument nr, >>>>>>> so all users which can set usage=1 will definitely have nr=1. >>>>>>> >>>>>>> int swap_duplicate(swp_entry_t entry) >>>>>>> { >>>>>>>         int err = 0; >>>>>>> >>>>>>>         while (!err && __swap_duplicate(entry, 1, 1) == -ENOMEM) >>>>>>>                 err = add_swap_count_continuation(entry, GFP_ATOMIC); >>>>>>>         return err; >>>>>>> } >>>>>> >>>>>> I understand that we don't have requirements to support "usage == 1 && >>>>>> nr > 1" case for __swap_duplicate() at least for now. >>>>>> >>>>>>> Maybe I can add a VM_WARN_ON to warn those people who might >>>>>>> want to extend swap_duplicate()? in that case, things could be quite >>>>>>> tricky. >>>>>>> >>>>>>> --- a/mm/swapfile.c >>>>>>> +++ b/mm/swapfile.c >>>>>>> @@ -3386,6 +3386,7 @@ static int __swap_duplicate(swp_entry_t entry, >>>>>>> unsigned char usage, int nr) >>>>>>> >>>>>>>         offset = swp_offset(entry); >>>>>>>         VM_WARN_ON(nr > SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER); >>>>>>> +       VM_WARN_ON(usage == 1 && nr > 1); >>>>>>>         ci = lock_cluster_or_swap_info(p, offset); >>>>>>> >>>>>>>         err = 0; >>>>>> >>>>>> Please add this.  And, I think that we need to make it explicit in patch >>>>>> description and comments to avoid potential confusing. >>>>> >>>>> cool. make sense to me. I will post something for Andrew to squash into. >>>>> >>>>>> >>>>>> And, because it's hard to implement the verify and change strategy if >>>>>> "usage == 1".  Can we only use that strategy for "usage == >>>>>> SWAP_HAS_CACHE"? >>>>> >>>>> I believe Baolin also needs the case for shmem. I don't feel a strong >>>>> need to split two logics(1 and non-1) as the code will be quite ugly :-) >>>> >>>> Don't need to split like that, it could be something like >>>> >>>>         for (i = 0; i < nr; i++) { >>>>                 if (usage == SWAP_HAS_CACHE) { >>>>                         /* Only verify for SWAP_HAS_CACHE */ >>>>                 } >>>>         } >>>> >>>>         for (i = 0; i < nr; i++) { >>>>                 if (usage == SWAP_HAS_CACHE) { >>>>                 } else { >>>>                         /* Verify and change for usage == 1 */ >>>>                 } >>>>         } >>>> >>> >>> but we also have cases where nr can be > 1 >>>         __swap_duplicate(entry, SWAP_MAP_SHMEM, 1); >> >> If we can do verification for "usage == SWAP_MAP_SHMEM", we can add that >> in the first loop. >> >> That is, we only do verification in the first loop, not do committing. >> In the second loop, we can ignore verifying if we have done that in the >> first loop. >> >> IMHO, this make code easier to be understood. > > Right. I believe the change below can help improve readability and also > clarify the swap_count_continued() case. > > diff --git a/mm/swapfile.c b/mm/swapfile.c > index 2fa29bdec171..75a89ce18edc 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -3538,6 +3538,7 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage, int nr) > > offset = swp_offset(entry); > VM_WARN_ON(nr > SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER); > + VM_WARN_ON(usage == 1 && nr > 1); > ci = lock_cluster_or_swap_info(p, offset); > > err = 0; > @@ -3564,17 +3565,9 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage, int nr) > err = -EEXIST; > else /* no users remaining */ > err = -ENOENT; > - > } else if (count || has_cache) { > - > - if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX) > - continue; > - else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX) > + if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX) > err = -EINVAL; > - else if (swap_count_continued(p, offset + i, count)) > - continue; > - else > - err = -ENOMEM; > } else > err = -ENOENT; /* unused swap entry */ > > @@ -3591,8 +3584,12 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage, int nr) > has_cache = SWAP_HAS_CACHE; > else if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX) > count += usage; > - else > + else if (swap_count_continued(p, offset + i, count)) > count = COUNT_CONTINUED; > + else { > + err = -ENOMEM; > + goto unlock_out; > + } > > WRITE_ONCE(p->swap_map[offset + i], count | has_cache); > } > > This makes the two iterations become: > > for (i = 0; i < nr; i++) { > count = p->swap_map[offset + i]; > > /* > * swapin_readahead() doesn't check if a swap entry is valid, so the > * swap entry could be SWAP_MAP_BAD. Check here with lock held. > */ > if (unlikely(swap_count(count) == SWAP_MAP_BAD)) { > err = -ENOENT; > goto unlock_out; > } > > has_cache = count & SWAP_HAS_CACHE; > count &= ~SWAP_HAS_CACHE; > > if (usage == SWAP_HAS_CACHE) { > /* set SWAP_HAS_CACHE if there is no cache and entry is used */ > if (!has_cache && count) > continue; > else if (has_cache) /* someone else added cache */ > err = -EEXIST; > else /* no users remaining */ > err = -ENOENT; > } else if (count || has_cache) { > if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX) > err = -EINVAL; > } else > err = -ENOENT; /* unused swap entry */ > > if (err) > goto unlock_out; > } > > for (i = 0; i < nr; i++) { > count = p->swap_map[offset + i]; > has_cache = count & SWAP_HAS_CACHE; > count &= ~SWAP_HAS_CACHE; > > if (usage == SWAP_HAS_CACHE) > has_cache = SWAP_HAS_CACHE; > else if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX) > count += usage; > else if (swap_count_continued(p, offset + i, count)) > count = COUNT_CONTINUED; > else { > err = -ENOMEM; > goto unlock_out; > } > > WRITE_ONCE(p->swap_map[offset + i], count | has_cache); > } > > Ying, do you feel more satisfied with the version above > compared to the code in mm-unstable? > > Baolin, I'd also appreciate it if you could re-test your > shmem case if Ying is okay with the enhancement above. Sure. I tested it with my shmem swap patches, and it still works as expected. Thanks.