From: Matthew Wilcox <willy@infradead.org>
To: Ryan Roberts <ryan.roberts@arm.com>
Cc: David Hildenbrand <david@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Huang Ying <ying.huang@intel.com>, Gao Xiang <xiang@kernel.org>,
Yu Zhao <yuzhao@google.com>, Yang Shi <shy828301@gmail.com>,
Michal Hocko <mhocko@suse.com>,
Kefeng Wang <wangkefeng.wang@huawei.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v3 1/4] mm: swap: Remove CLUSTER_FLAG_HUGE from swap_cluster_info:flags
Date: Fri, 1 Mar 2024 16:31:12 +0000 [thread overview]
Message-ID: <ZeIC0Bn7N0JlP4TY@casper.infradead.org> (raw)
In-Reply-To: <5ebac77a-5c61-481f-8ac1-03bc4f4e2b1d@arm.com>
On Fri, Mar 01, 2024 at 04:27:32PM +0000, Ryan Roberts wrote:
> I've implemented the batching as David suggested, and I'm pretty confident it's
> correct. The only problem is that during testing I can't provoke the code to
> take the path. I've been pouring through the code but struggling to figure out
> under what situation you would expect the swap entry passed to
> free_swap_and_cache() to still have a cached folio? Does anyone have any idea?
>
> This is the original (unbatched) function, after my change, which caused David's
> concern that we would end up calling __try_to_reclaim_swap() far too much:
>
> int free_swap_and_cache(swp_entry_t entry)
> {
> struct swap_info_struct *p;
> unsigned char count;
>
> if (non_swap_entry(entry))
> return 1;
>
> p = _swap_info_get(entry);
> if (p) {
> count = __swap_entry_free(p, entry);
> if (count == SWAP_HAS_CACHE)
> __try_to_reclaim_swap(p, swp_offset(entry),
> TTRS_UNMAPPED | TTRS_FULL);
> }
> return p != NULL;
> }
>
> The trouble is, whenever its called, count is always 0, so
> __try_to_reclaim_swap() never gets called.
>
> My test case is allocating 1G anon memory, then doing madvise(MADV_PAGEOUT) over
> it. Then doing either a munmap() or madvise(MADV_FREE), both of which cause this
> function to be called for every PTE, but count is always 0 after
> __swap_entry_free() so __try_to_reclaim_swap() is never called. I've tried for
> order-0 as well as PTE- and PMD-mapped 2M THP.
I think you have to page it back in again, then it will have an entry in
the swap cache. Maybe. I know little about anon memory ;-)
If that doesn't work, perhaps use tmpfs, and use some memory pressure to
force that to swap?
> I'm guessing the swapcache was already reclaimed as part of MADV_PAGEOUT? I'm
> using a block ram device as my backing store - I think this does synchronous IO
> so perhaps if I have a real block device with async IO I might have more luck?
> Just a guess...
>
> Or perhaps this code path is a corner case? In which case, perhaps its not worth
> adding the batching optimization after all?
>
> Thanks,
> Ryan
>
next prev parent reply other threads:[~2024-03-01 16:31 UTC|newest]
Thread overview: 116+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-25 14:45 [PATCH v3 0/4] Swap-out small-sized THP without splitting Ryan Roberts
2023-10-25 14:45 ` [PATCH v3 1/4] mm: swap: Remove CLUSTER_FLAG_HUGE from swap_cluster_info:flags Ryan Roberts
2024-02-22 10:19 ` David Hildenbrand
2024-02-22 10:20 ` David Hildenbrand
2024-02-26 17:41 ` Ryan Roberts
2024-02-27 17:10 ` Ryan Roberts
2024-02-27 19:17 ` David Hildenbrand
2024-02-28 9:37 ` Ryan Roberts
2024-02-28 12:12 ` David Hildenbrand
2024-02-28 14:57 ` Ryan Roberts
2024-02-28 15:12 ` David Hildenbrand
2024-02-28 15:18 ` Ryan Roberts
2024-03-01 16:27 ` Ryan Roberts
2024-03-01 16:31 ` Matthew Wilcox [this message]
2024-03-01 16:44 ` Ryan Roberts
2024-03-01 17:00 ` David Hildenbrand
2024-03-01 17:14 ` Ryan Roberts
2024-03-01 17:18 ` David Hildenbrand
2024-03-01 17:06 ` Ryan Roberts
2024-03-04 4:52 ` Barry Song
2024-03-04 5:42 ` Barry Song
2024-03-05 7:41 ` Ryan Roberts
2024-03-01 16:31 ` Ryan Roberts
2024-03-01 16:32 ` David Hildenbrand
2024-03-04 16:03 ` Ryan Roberts
2024-03-04 17:30 ` David Hildenbrand
2024-03-04 18:38 ` Ryan Roberts
2024-03-04 20:50 ` David Hildenbrand
2024-03-04 21:55 ` Ryan Roberts
2024-03-04 22:02 ` David Hildenbrand
2024-03-04 22:34 ` Ryan Roberts
2024-03-05 6:11 ` Huang, Ying
2024-03-05 8:35 ` David Hildenbrand
2024-03-05 8:46 ` Ryan Roberts
2024-02-28 13:33 ` Matthew Wilcox
2024-02-28 14:24 ` Ryan Roberts
2024-02-28 14:59 ` Ryan Roberts
2023-10-25 14:45 ` [PATCH v3 2/4] mm: swap: Remove struct percpu_cluster Ryan Roberts
2023-10-25 14:45 ` [PATCH v3 3/4] mm: swap: Simplify ssd behavior when scanner steals entry Ryan Roberts
2023-10-25 14:45 ` [PATCH v3 4/4] mm: swap: Swap-out small-sized THP without splitting Ryan Roberts
2023-10-30 8:18 ` Huang, Ying
2023-10-30 13:59 ` Ryan Roberts
2023-10-31 8:12 ` Huang, Ying
2023-11-03 11:42 ` Ryan Roberts
2023-11-02 7:40 ` Barry Song
2023-11-02 10:21 ` Ryan Roberts
2023-11-02 22:36 ` Barry Song
2023-11-03 11:31 ` Ryan Roberts
2023-11-03 13:57 ` Steven Price
2023-11-04 9:34 ` Barry Song
2023-11-06 10:12 ` Steven Price
2023-11-06 21:39 ` Barry Song
2023-11-08 11:51 ` Steven Price
2023-11-07 12:46 ` Ryan Roberts
2023-11-07 18:05 ` Barry Song
2023-11-08 11:23 ` Barry Song
2023-11-08 20:20 ` Ryan Roberts
2023-11-08 21:04 ` Barry Song
2023-11-04 5:49 ` Barry Song
2024-02-05 9:51 ` Barry Song
2024-02-05 12:14 ` Ryan Roberts
2024-02-18 23:40 ` Barry Song
2024-02-20 20:03 ` Ryan Roberts
2024-03-05 9:00 ` Ryan Roberts
2024-03-05 9:54 ` Barry Song
2024-03-05 10:44 ` Ryan Roberts
2024-02-27 12:28 ` Ryan Roberts
2024-02-27 13:37 ` Ryan Roberts
2024-02-28 2:46 ` Barry Song
2024-02-22 7:05 ` Barry Song
2024-02-22 10:09 ` David Hildenbrand
2024-02-23 9:46 ` Barry Song
2024-02-27 12:05 ` Ryan Roberts
2024-02-28 1:23 ` Barry Song
2024-02-28 9:34 ` David Hildenbrand
2024-02-28 23:18 ` Barry Song
2024-02-28 15:57 ` Ryan Roberts
2023-11-29 7:47 ` [PATCH v3 0/4] " Barry Song
2023-11-29 12:06 ` Ryan Roberts
2023-11-29 20:38 ` Barry Song
2024-01-18 11:10 ` [PATCH RFC 0/6] mm: support large folios swap-in Barry Song
2024-01-18 11:10 ` [PATCH RFC 1/6] arm64: mm: swap: support THP_SWAP on hardware with MTE Barry Song
2024-01-26 23:14 ` Chris Li
2024-02-26 2:59 ` Barry Song
2024-01-18 11:10 ` [PATCH RFC 2/6] mm: swap: introduce swap_nr_free() for batched swap_free() Barry Song
2024-01-26 23:17 ` Chris Li
2024-02-26 4:47 ` Barry Song
2024-01-18 11:10 ` [PATCH RFC 3/6] mm: swap: make should_try_to_free_swap() support large-folio Barry Song
2024-01-26 23:22 ` Chris Li
2024-01-18 11:10 ` [PATCH RFC 4/6] mm: support large folios swapin as a whole Barry Song
2024-01-27 19:53 ` Chris Li
2024-02-26 7:29 ` Barry Song
2024-01-27 20:06 ` Chris Li
2024-02-26 7:31 ` Barry Song
2024-01-18 11:10 ` [PATCH RFC 5/6] mm: rmap: weaken the WARN_ON in __folio_add_anon_rmap() Barry Song
2024-01-18 11:54 ` David Hildenbrand
2024-01-23 6:49 ` Barry Song
2024-01-29 3:25 ` Chris Li
2024-01-29 10:06 ` David Hildenbrand
2024-01-29 16:31 ` Chris Li
2024-02-26 5:05 ` Barry Song
2024-04-06 23:27 ` Barry Song
2024-01-27 23:41 ` Chris Li
2024-01-18 11:10 ` [PATCH RFC 6/6] mm: madvise: don't split mTHP for MADV_PAGEOUT Barry Song
2024-01-29 2:15 ` Chris Li
2024-02-26 6:39 ` Barry Song
2024-02-27 12:22 ` Ryan Roberts
2024-02-27 22:39 ` Barry Song
2024-02-27 14:40 ` Ryan Roberts
2024-02-27 18:57 ` Barry Song
2024-02-28 3:49 ` Barry Song
2024-01-18 15:25 ` [PATCH RFC 0/6] mm: support large folios swap-in Ryan Roberts
2024-01-18 23:54 ` Barry Song
2024-01-19 13:25 ` Ryan Roberts
2024-01-27 14:27 ` Barry Song
2024-01-29 9:05 ` Huang, Ying
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