On 29/01/2024 12:46, David Hildenbrand wrote: > Now that the rmap overhaul[1] is upstream that provides a clean interface > for rmap batching, let's implement PTE batching during fork when processing > PTE-mapped THPs. > > This series is partially based on Ryan's previous work[2] to implement > cont-pte support on arm64, but its a complete rewrite based on [1] to > optimize all architectures independent of any such PTE bits, and to > use the new rmap batching functions that simplify the code and prepare > for further rmap accounting changes. > > We collect consecutive PTEs that map consecutive pages of the same large > folio, making sure that the other PTE bits are compatible, and (a) adjust > the refcount only once per batch, (b) call rmap handling functions only > once per batch and (c) perform batch PTE setting/updates. > > While this series should be beneficial for adding cont-pte support on > ARM64[2], it's one of the requirements for maintaining a total mapcount[3] > for large folios with minimal added overhead and further changes[4] that > build up on top of the total mapcount. > > Independent of all that, this series results in a speedup during fork with > PTE-mapped THP, which is the default with THPs that are smaller than a PMD > (for example, 16KiB to 1024KiB mTHPs for anonymous memory[5]). > > On an Intel Xeon Silver 4210R CPU, fork'ing with 1GiB of PTE-mapped folios > of the same size (stddev < 1%) results in the following runtimes > for fork() (shorter is better): > > Folio Size | v6.8-rc1 | New | Change > ------------------------------------------ > 4KiB | 0.014328 | 0.014035 | - 2% > 16KiB | 0.014263 | 0.01196 | -16% > 32KiB | 0.014334 | 0.01094 | -24% > 64KiB | 0.014046 | 0.010444 | -26% > 128KiB | 0.014011 | 0.010063 | -28% > 256KiB | 0.013993 | 0.009938 | -29% > 512KiB | 0.013983 | 0.00985 | -30% > 1024KiB | 0.013986 | 0.00982 | -30% > 2048KiB | 0.014305 | 0.010076 | -30% Just a heads up that I'm seeing some strange results on Apple M2. Fork for order-0 is seemingly costing ~17% more. I'm using GCC 13.2 and was pretty sure I didn't see this problem with version 1; although that was on a different baseline and I've thrown the numbers away so will rerun and try to debug this. | kernel | mean_rel | std_rel | |:------------|-----------:|----------:| | mm-unstable | 0.0% | 1.1% | | patch 1 | -2.3% | 1.3% | | patch 10 | -2.9% | 2.7% | | patch 11 | 13.5% | 0.5% | | patch 12 | 15.2% | 1.2% | | patch 13 | 18.2% | 0.7% | | patch 14 | 20.5% | 1.0% | | patch 15 | 17.1% | 1.6% | | patch 15 | 16.7% | 0.8% | fork for order-9 is looking good (-20%), and for the zap series, munmap is looking good, but dontneed is looking poor for both order-0 and 9. But one thing at a time... let's concentrate on fork order-0 first. Note that I'm still using the "old" benchmark code. Could you resend me the link to the new code? Although I don't think there should be any effect for order-0 anyway, if I understood your changes correctly? > > Note that these numbers are even better than the ones from v1 (verified > over multiple reboots), even though there were only minimal code changes. > Well, I removed a pte_mkclean() call for anon folios, maybe that also > plays a role. > > But my experience is that fork() is extremely sensitive to code size, > inlining, ... so I suspect we'll see on other architectures rather a change > of -20% instead of -30%, and it will be easy to "lose" some of that speedup > in the future by subtle code changes. > > Next up is PTE batching when unmapping. Only tested on x86-64. > Compile-tested on most other architectures. > > v2 -> v3: > * Rebased on mm-unstable > * Picked up RB's > * Updated documentation of wrprotect_ptes(). > > v1 -> v2: > * "arm64/mm: Make set_ptes() robust when OAs cross 48-bit boundary" > -> Added patch from Ryan > * "arm/pgtable: define PFN_PTE_SHIFT" > -> Removed the arm64 bits > * "mm/pgtable: make pte_next_pfn() independent of set_ptes()" > * "arm/mm: use pte_next_pfn() in set_ptes()" > * "powerpc/mm: use pte_next_pfn() in set_ptes()" > -> Added to use pte_next_pfn() in some arch set_ptes() implementations > I tried to make use of pte_next_pfn() also in the others, but it's > not trivial because the other archs implement set_ptes() in their > asm/pgtable.h. Future work. > * "mm/memory: factor out copying the actual PTE in copy_present_pte()" > -> Move common folio_get() out of if/else > * "mm/memory: optimize fork() with PTE-mapped THP" > -> Add doc for wrprotect_ptes > -> Extend description to mention handling of pinned folios > -> Move common folio_ref_add() out of if/else > * "mm/memory: ignore dirty/accessed/soft-dirty bits in folio_pte_batch()" > -> Be more conservative with dirt/soft-dirty, let the caller specify > using flags > > [1] https://lkml.kernel.org/r/20231220224504.646757-1-david@xxxxxxxxxx > [2] https://lkml.kernel.org/r/20231218105100.172635-1-ryan.roberts@xxxxxxx > [3] https://lkml.kernel.org/r/20230809083256.699513-1-david@xxxxxxxxxx > [4] https://lkml.kernel.org/r/20231124132626.235350-1-david@xxxxxxxxxx > [5] https://lkml.kernel.org/r/20231207161211.2374093-1-ryan.roberts@xxxxxxx > > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> > Cc: Ryan Roberts <ryan.roberts@xxxxxxx> > Cc: Russell King <linux@xxxxxxxxxxxxxxx> > Cc: Catalin Marinas <catalin.marinas@xxxxxxx> > Cc: Will Deacon <will@xxxxxxxxxx> > Cc: Dinh Nguyen <dinguyen@xxxxxxxxxx> > Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx> > Cc: Nicholas Piggin <npiggin@xxxxxxxxx> > Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx> > Cc: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxx> > Cc: "Naveen N. Rao" <naveen.n.rao@xxxxxxxxxxxxx> > Cc: Paul Walmsley <paul.walmsley@xxxxxxxxxx> > Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx> > Cc: Albert Ou <aou@xxxxxxxxxxxxxxxxx> > Cc: Alexander Gordeev <agordeev@xxxxxxxxxxxxx> > Cc: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx> > Cc: Heiko Carstens <hca@xxxxxxxxxxxxx> > Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx> > Cc: Christian Borntraeger <borntraeger@xxxxxxxxxxxxx> > Cc: Sven Schnelle <svens@xxxxxxxxxxxxx> > Cc: "David S. Miller" <davem@xxxxxxxxxxxxx> > Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > Cc: linuxppc-dev@xxxxxxxxxxxxxxxx > Cc: linux-riscv@xxxxxxxxxxxxxxxxxxx > Cc: linux-s390@xxxxxxxxxxxxxxx > Cc: sparclinux@xxxxxxxxxxxxxxx > > --- > > Andrew asked for a resend based on latest mm-unstable. I am sending this > out earlier than I would usually have sent out the next version, so we can > pull it into mm-unstable again now that v1 was dropped. > > David Hildenbrand (14): > arm/pgtable: define PFN_PTE_SHIFT > nios2/pgtable: define PFN_PTE_SHIFT > powerpc/pgtable: define PFN_PTE_SHIFT > riscv/pgtable: define PFN_PTE_SHIFT > s390/pgtable: define PFN_PTE_SHIFT > sparc/pgtable: define PFN_PTE_SHIFT > mm/pgtable: make pte_next_pfn() independent of set_ptes() > arm/mm: use pte_next_pfn() in set_ptes() > powerpc/mm: use pte_next_pfn() in set_ptes() > mm/memory: factor out copying the actual PTE in copy_present_pte() > mm/memory: pass PTE to copy_present_pte() > mm/memory: optimize fork() with PTE-mapped THP > mm/memory: ignore dirty/accessed/soft-dirty bits in folio_pte_batch() > mm/memory: ignore writable bit in folio_pte_batch() > > Ryan Roberts (1): > arm64/mm: Make set_ptes() robust when OAs cross 48-bit boundary > > arch/arm/include/asm/pgtable.h | 2 + > arch/arm/mm/mmu.c | 2 +- > arch/arm64/include/asm/pgtable.h | 28 ++-- > arch/nios2/include/asm/pgtable.h | 2 + > arch/powerpc/include/asm/pgtable.h | 2 + > arch/powerpc/mm/pgtable.c | 5 +- > arch/riscv/include/asm/pgtable.h | 2 + > arch/s390/include/asm/pgtable.h | 2 + > arch/sparc/include/asm/pgtable_64.h | 2 + > include/linux/pgtable.h | 33 ++++- > mm/memory.c | 212 ++++++++++++++++++++++------ > 11 files changed, 229 insertions(+), 63 deletions(-) > > > base-commit: d162e170f1181b4305494843e1976584ddf2b72e
