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[2003:cb:c733:7c00:d067:e327:4f99:7546]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-431bd9403bfsm14911565e9.21.2024.10.30.02.01.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 30 Oct 2024 02:01:38 -0700 (PDT) Message-ID: <8d9dc103-47c5-4719-971a-31efb091432a@redhat.com> Date: Wed, 30 Oct 2024 10:01:37 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/gup: restore the ability to pin more than 2GB at a time From: David Hildenbrand To: John Hubbard , Alistair Popple Cc: Christoph Hellwig , Andrew Morton , LKML , linux-mm@kvack.org, linux-stable@vger.kernel.org, Vivek Kasireddy , Dave Airlie , Gerd Hoffmann , Matthew Wilcox , Jason Gunthorpe , Peter Xu , Arnd Bergmann , Daniel Vetter , Dongwon Kim , Hugh Dickins , Junxiao Chang , Mike Kravetz , Oscar Salvador References: <20241030030116.670307-1-jhubbard@nvidia.com> <249d2614-0bcc-4ca8-b24e-7c0578a81dce@nvidia.com> <87r07yp0ng.fsf@nvdebian.thelocal> <128d04dd-2d48-4a98-8537-49589b4db1c3@nvidia.com> Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: wmxr5n776qcyo7w8ccza57cigaa7kpbu X-Rspamd-Queue-Id: 793FB1C0030 X-Rspamd-Server: rspam02 X-HE-Tag: 1730278871-477170 X-HE-Meta: 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 niviuT9z BVlPnA8n+OCXrrVJhNK3GiBg3vFW7cwKZbuZlf8Gp+cF7/RCct8jGGARwld2RpEp2hpNFTBPrV+v36JE+kU+Dk/07kzNCVPUYt6xcvevbGqfC9mgH99RVMztIAZ0kVfuHIZk9pDAhEeslqLAchHibWJz2YngkfM8uhNt3NgLwrvpsIYYWtRInb2BNfbOZCYSHZCTE+BH7+1dawKDR1g3BNGwMrcstCgGzpOhoQClQnPSyaUYiz+8VXxIaU6Do9orelXx1uvVCliC2glMntkkRVROWYalcWX8ZkjC1EyYg5Uws7lVFjVdPTnBd1UIJAm79eGZCfkF1JFK6u1BZ6cAeIdCYlvqYyX+CWQLxAcye7hn/tcFsOBCmP/VqqXKs/GGHCSO+boCje1XU3Tj0pEOZVjYnp3zC0Qu/BM+fZ7JMyaeiq4m6SaLYxtiRG3WE/cmWKCNDTiKV+qSjzpNvkJwR5Lj6AhnByyAs3cgX 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 30.10.24 09:34, David Hildenbrand wrote: > On 30.10.24 07:50, John Hubbard wrote: >> On 10/29/24 11:18 PM, Alistair Popple wrote: >>> John Hubbard writes: >>>> On 10/29/24 9:42 PM, Christoph Hellwig wrote: >>>>> On Tue, Oct 29, 2024 at 09:39:15PM -0700, John Hubbard wrote: >> ... >>>>> Because pinning down these amounts of memoryt is completely insane. >>>>> I don't mind the switch to kvmalloc, but we need to put in an upper >>>>> bound of what can be pinned. >>>> >>>> I'm wondering though, how it is that we decide how much of the user's >>>> system we prevent them from using? :) People with hardware accelerators >>>> do not always have page fault capability, and yet these troublesome >>>> users insist on stacking their system full of DRAM and then pointing >>>> the accelerator to it. >>>> >>>> How would we choose a value? Memory sizes keep going up... >>> >>> The obvious answer is you let users decide. I did have a patch series to >>> do that via a cgroup[1]. However I dropped that series mostly because I >>> couldn't find any users of such a limit to provide feedback on how they >>> would use it or how they wanted it to work. >>> >> >> Trawling through the discussion there, I see that Jason Gunthorpe mentioned: >> >> "Things like VFIO & KVM use cases effectively pin 90% of all system memory" > > The unusual thing is not the amount of system memory we are pinning but > *how many* pages we try pinning in the single call. > > If you stare at vfio_pin_pages_remote, we seem to be batching it. > > long req_pages = min_t(long, npage, batch->capacity); > > Which is > > #define VFIO_BATCH_MAX_CAPACITY (PAGE_SIZE / sizeof(struct page *)) > > > So you can fix this in your driver ;) > > > We should maybe try a similar limit internally: if you call > pin_user_pages_remote() with a large number, we'll cap it at some magic > value (similar to above). The caller will simply realize that not all > pages were pinned and will retry. > > See get_user_pages_remote(): "Returns either number of pages pinned > (which may be less than the number requested), or an error. Details > about the return value:" > > > Alternatively, I recall there was a way to avoid the temporary > allocation ... let me hack up a prototype real quick. Completely untested (also note the interesting TODO): From a23984b4f1a39ec984489fbe16708aedf4f9db95 Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Wed, 30 Oct 2024 10:00:50 +0100 Subject: [PATCH] tmp Signed-off-by: David Hildenbrand --- mm/gup.c | 120 ++++++++++++++++++++++++++++++++++++------------------- 1 file changed, 78 insertions(+), 42 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index a82890b46a36..8807b36c2363 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2273,20 +2273,56 @@ struct page *get_dump_page(unsigned long addr) #endif /* CONFIG_ELF_CORE */ #ifdef CONFIG_MIGRATION + +/* + * An array of either pages or folios. While we could currently interpret a + * list of folios like a list of pages, it would only work as long as + * "struct folio" overlays "struct page" -- and it would not allow for + * avoiding page_folio() calls. + */ +struct pages_or_folios { + union { + struct page **pages; + struct folio **folios; + void **entries; + }; + bool has_folios; + long nr_entries; +}; + +static struct folio *pofs_get_folio(struct pages_or_folios *pofs, long i) +{ + if (pofs->has_folios) + return pofs->folios[i]; + return page_folio(pofs->pages[i]); +} + +static void pofs_clear_entry(struct pages_or_folios *pofs, long i) +{ + pofs->entries[i] = NULL; +} + +static void pofs_unpin(struct pages_or_folios *pofs) +{ + if (pofs->has_folios) + unpin_folios(pofs->folios, pofs->nr_entries); + else + unpin_user_pages(pofs->pages, pofs->nr_entries); +} + /* * Returns the number of collected folios. Return value is always >= 0. */ static unsigned long collect_longterm_unpinnable_folios( - struct list_head *movable_folio_list, - unsigned long nr_folios, - struct folio **folios) + struct list_head *movable_folio_list, + struct pages_or_folios *pofs) { unsigned long i, collected = 0; struct folio *prev_folio = NULL; bool drain_allow = true; - for (i = 0; i < nr_folios; i++) { - struct folio *folio = folios[i]; + for (i = 0; i < pofs->nr_entries; i++) { + struct folio *folio = pofs_get_folio(pofs, i); if (folio == prev_folio) continue; @@ -2310,6 +2346,11 @@ static unsigned long collect_longterm_unpinnable_folios( drain_allow = false; } + /* + * TODO: if isolation fails we might already have it in the + * list, if pages of different folios are interleaved + * (e.g., COW). We might want to check all entries in the list. + */ if (!folio_isolate_lru(folio)) continue; @@ -2328,15 +2369,14 @@ static unsigned long collect_longterm_unpinnable_folios( * failure (or partial success). */ static int migrate_longterm_unpinnable_folios( - struct list_head *movable_folio_list, - unsigned long nr_folios, - struct folio **folios) + struct list_head *movable_folio_list, + struct pages_or_folios *pofs) { int ret; unsigned long i; - for (i = 0; i < nr_folios; i++) { - struct folio *folio = folios[i]; + for (i = 0; i < pofs->nr_entries; i++) { + struct folio *folio = pofs_get_folio(pofs, i); if (folio_is_device_coherent(folio)) { /* @@ -2344,7 +2384,7 @@ static int migrate_longterm_unpinnable_folios( * convert the pin on the source folio to a normal * reference. */ - folios[i] = NULL; + pofs_clear_entry(pofs, i); folio_get(folio); gup_put_folio(folio, 1, FOLL_PIN); @@ -2363,8 +2403,8 @@ static int migrate_longterm_unpinnable_folios( * calling folio_isolate_lru() which takes a reference so the * folio won't be freed if it's migrating. */ - unpin_folio(folios[i]); - folios[i] = NULL; + unpin_folio(pofs_get_folio(pofs, i)); + pofs_clear_entry(pofs, i); } if (!list_empty(movable_folio_list)) { @@ -2387,12 +2427,24 @@ static int migrate_longterm_unpinnable_folios( return -EAGAIN; err: - unpin_folios(folios, nr_folios); + pofs_unpin(pofs); putback_movable_pages(movable_folio_list); return ret; } +static long check_and_migrate_movable_pages_or_folios(struct pages_or_folios *pofs) +{ + LIST_HEAD(movable_folio_list); + unsigned long collected; + + collected = collect_longterm_unpinnable_folios(&movable_folio_list, pofs); + if (!collected) + return 0; + + return migrate_longterm_unpinnable_folios(&movable_folio_list, pofs); +} + /* * Check whether all folios are *allowed* to be pinned indefinitely (longterm). * Rather confusingly, all folios in the range are required to be pinned via @@ -2412,41 +2464,25 @@ static int migrate_longterm_unpinnable_folios( static long check_and_migrate_movable_folios(unsigned long nr_folios, struct folio **folios) { - unsigned long collected; - LIST_HEAD(movable_folio_list); - - collected = collect_longterm_unpinnable_folios(&movable_folio_list, - nr_folios, folios); - if (!collected) - return 0; + struct pages_or_folios pofs = { + .folios = folios, + .has_folios = true, + .nr_entries = nr_folios, + }; - return migrate_longterm_unpinnable_folios(&movable_folio_list, - nr_folios, folios); + return check_and_migrate_movable_pages_or_folios(&pofs); } -/* - * This routine just converts all the pages in the @pages array to folios and - * calls check_and_migrate_movable_folios() to do the heavy lifting. - * - * Please see the check_and_migrate_movable_folios() documentation for details. - */ +/* See check_and_migrate_movable_folios(). */ static long check_and_migrate_movable_pages(unsigned long nr_pages, struct page **pages) { - struct folio **folios; - long i, ret; + struct pages_or_folios pofs = { + .pages = pages, + .nr_entries = nr_pages, + }; - folios = kmalloc_array(nr_pages, sizeof(*folios), GFP_KERNEL); - if (!folios) - return -ENOMEM; - - for (i = 0; i < nr_pages; i++) - folios[i] = page_folio(pages[i]); - - ret = check_and_migrate_movable_folios(nr_pages, folios); - - kfree(folios); - return ret; + return check_and_migrate_movable_pages_or_folios(&pofs); } #else static long check_and_migrate_movable_pages(unsigned long nr_pages, -- 2.47.0 -- Cheers, David / dhildenb