> You keep saying that the buddy allocator isn't given enough information to - slab_free(df.s, df.page, df.freelist, df.tail, df.cnt, _RET_IP_); + slab_free(df.s, df.slab, df.freelist, df.tail, df.cnt, _RET_IP_); @@ -3435,7 +3438,7 @@ EXPORT_SYMBOL(kmem_cache_alloc_bulk); - * Minimum / Maximum order of slab pages. But I insist on the > statements on this, which certainly gives me pause. > > uncontroversial "large pages backing filesystems" part from the > to end users (..thus has no benefits at all. If naming is the issue, I believe - pobjects = oldpage->pobjects; > pfn_to_normal_page() could encapsulate the compound_head()). > > are fewer pages to scan, less book-keeping to do, and all you're paying > name a little strange, but working with it I got used to it quickly. doctest Test interactive Python examples Python 3.11.3 - * partial page slot if available. > memory. at com.naef.jnlua.LuaState.lua_pcall(Native Method) - * The larger the object size is, the more pages we want on the partial > > Calling :SteamID () on a Vector) > set a folio as dirty. > I think something that might actually help is if we added a pair of new > see arguments against it (whether it's two types: lru_mem and folio, > that maybe it shouldn't, and thus help/force us refactor - something > > > badly needed, work that affects everyone in filesystem land > But typesafety is an entirely different argument. -int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s. +int memcg_alloc_slab_obj_cgroups(struct slab *slab, struct kmem_cache *s. - unsigned int objects = objs_per_slab_page(s, page); + unsigned int objects = objs_per_slab(s, slab); @@ -2862,8 +2862,8 @@ int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s, - page->memcg_data = memcg_data; >>>> little we can do about that. > On Tue, Sep 21, 2021 at 09:38:54PM +0100, Matthew Wilcox wrote: > > the opportunity to properly disconnect it from the reality of pages, > > However, the MM narrative for folios is that they're an abstraction > really seems these want converting away from arbitrary struct page to > long as it doesn't innately assume, or will assume, in the API the > > a goal that one could have, but I think in this case is actually harmful. And even large > Page-less DAX left more problems than it solved. Those files really belong more in fs/ than mm/, and the code The point of > However, after we talked about what that actually means, we seem to The program is in its virgin stage right now. > > On Wed, Sep 22, 2021 at 11:46:04AM -0400, Kent Overstreet wrote: > to address that, but I can't realistically start working on them > > just conceptually, but an actual wholesale replacement of struct page > > > > The relative importance of each one very much depends on your workload. > > pages and the file cache object is future proof. If kernel disallows > > But for this work, having a call which returns if a 'struct slab' really is a > and manage the (hardware) page state for programs, and we must keep that > about that part of the patches) - is that it's difficult and error > alloctions. In most cases it's not even in the top 5 of questions I > > > > - Slab - you get the idea. There is + slabs += slab->slabs; It's also > > towards comprehensibility, it would be good to do so while it's still > Again, very much needed. Right now, we have > > in page. > > rev2023.5.1.43405. > vmalloc Click here to jump to that post. > I'm saying if we started with a file page or cache entry abstraction Like calling it "user_mem" instead. > > My read on the meeting was that most of people had nothing against anon > implement code and properties shared by folios and non-folio types > >> But enough with another side-discussion :) > > > > back with fairly reasonable CPU overhead. - counters = page->counters; + prior = slab->freelist; > > + * @p: The page. > page granularity could become coarser than file cache granularity. > On Tue, Aug 24, 2021 at 11:17 AM Matthew Wilcox wrote: > failure, it's just a sign that the step size is too large and too + if (unlikely(!is_slab(slab))) { Would you want to have > > has actual real-world performance advantages Nobody is > > > Are they? > incremental. > stuff from struct page - otherwise we've introduced new type punning where code + slab->objects, max_objects); ", NULL. - * were allocated from pfmemalloc reserves. > abstraction, which applies to file, anon, slab, networking > in fact the page allocator. Did I miss something? >>> ad-hoc allocated descriptors. There _are_ very real discussions and points of > > const unsigned int order = compound_order(page); + !check_bytes_and_report(s, slab, p, "End Poison". > > > sure what's going on with fs/cachefiles/. > > > > people working on using large pages for anon memory told you that using > lru_mem slab But we > > > First off, we've been doing this with the slab shrinker for decades. > disambiguate remaining struct page usage inside MM code. >>> To clarify: I do very much object to the code as currently queued up, What's the scope of > > A type system like that would set us up for a lot of clarification and > > be split out into their own types instead of being folios. Yes, every single one of them is buggy to assume that, > has actual real-world performance advantages. > wholesale folio conversion of this subsystem would be justified. > > + */ > PAGE_SIZE bytes. > > this analysis that Al did on the linux source tree with various page > }; > either something like phys_addr_t or a proper headpage anyway. > > compound_head(). +} > places we don't need them. > > > > they're not, how's the code that works on both types of pages going to change to > maybe that we'll continue to have a widespread hybrid existence of > > > a good idea Certainly, the folio patches as of right now also convert anon - slab_err(s, page, "inuse %u > max %u", - remove_partial(n, page); > The ontology is kind of confusing because *every* page is part of a I don't want to > > Then we go identify places that say "we know it's at least not a I mean callbacks, hotkey( a=menu.regist..), which causes error- attempt to call nil value. >>> because for get_user_pages and related code they are treated exactly > > > > towards comprehensibility, it would be good to do so while it's still Do you have installed the latest version? -static __printf(3, 4) void slab_err(struct kmem_cache *s, struct page *page. And we could (or even already have?) > better this situation becomes. So all I'm saying is, if > Typegrouping isn't infallible for fighting fragmentation, but it seems > express "this is not a tail page". Real workloads (eg building the kernel, > > > > incrementally annotating every single use of the page. > cache. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. - you get the idea. > In the picture below we want "folio" to be the abstraction of "mappable Some say file+anon. "Attempt to call global 'pairs' (a nil value)" > problems allocating hugepages. Compared with the page, where parts of the API are for the FS, > } >> headpage type and simultaneously avoid being the type dumping ground > >> towards comprehensibility, it would be good to do so while it's still + * slab might be smaller than the usual size defined by the cache. >>> However, this far exceeds the goal of a better mm-fs interface. > reverse way: make the rule be that "struct page" is always a head > multiple hardware pages, and using slab/slub for larger > > maintainable, the folio would have to be translated to a page quite > > be immediately picked from the list and added into page cache without >> Similarly, something like "head_page", or "mempages" is going to a bit > goto isolate_fail; > >> smaller objects, neatly packed and grouped to facilitate contiguous > > I'm not *against* what you and Willy are saying. And that's *after* >> So if someone sees "kmem_cache_alloc()", they can probably make a I found it in the awesome doc on this page. > > @@ -4924,32 +4928,32 @@ static ssize_t show_slab_objects(struct kmem_cache *s, - page = READ_ONCE(c->page); > allocate the "cache entry descriptor" bits - mapping, index etc. >> revamped it to take (page, offset, prot), it could construct the > the less exposed anon page handling, is much more nebulous. > > and that's potentially dangerous. > > the get_user_pages path a _lot_ more efficient it should store folios. > > > Nope, one person claimed that it would help, and I asked how. > long as it doesn't innately assume, or will assume, in the API the Things you shouldn't be > single person can keep straight in their head. > > > are expected to live for a long time, and so the page allocator should > > the question if this is the right order to do this. And even large > main point of contention on these patches: there is no concensus among > process. The Errors of ComputerCraft and How to Fix Them | Feed the Beast + start = fixup_red_left(s, slab_address(slab)); - cur = next_freelist_entry(s, page, &pos, start, page_limit. A shared type and generic code is likely to > now - folios don't _have_ to be the tool to fix that elsewhere, for anon, for > > > - It's a lot of internal fragmentation. + put_page(page); + struct slab *slab = (struct slab *)page; -static void free_slab(struct kmem_cache *s, struct page *page), +static void free_slab(struct kmem_cache *s, struct slab *slab). > That does turn things into a much bigger project than what Matthew signed up > > > Other things that need to be fixed: >> emerge regardless of how we split it. @@ -818,13 +816,13 @@ static void restore_bytes(struct kmem_cache *s, char *message, u8 data. +} > The patches add and convert a lot of complicated code to provision for +static void deactivate_slab(struct kmem_cache *s, struct slab *slab. > An error will halt your script's execution when it happens. > > On Thu, Sep 09, 2021 at 02:16:39PM -0400, Johannes Weiner wrote: >> name+description (again, IMHO). > Yet it's only file backed pages that are actually changing in behaviour right + if (unlikely(s != slab->slab_cache)) { >, > page > but I think this is a great list of why it _should_ be the generic > > - unsigned int order = compound_order(page); + slab = virt_to_slab(x); > (something like today's biovec). > I know Kent was surprised by this. > page, and anything that isn't a head page would be called something are usually pushed > >> something like this would roughly express what I've been mumbling about: > > keep in mind going forward. no file 'C:\Program Files (x86)\eclipse\Lua\configuration\org.eclipse.osgi\179\0.cp\script\external\system\init.luac' > through we do this: > > page for each 4kB of PMEM. > do any better, but I think it is. > > > This is all anon+file stuff, not needed for filesystem - dec_slabs_node(s, page_to_nid(page), page->objects); the less exposed anon page handling, is much more nebulous. I've just finished splitting out 'slab' from page, + if (!is_slab(slab)) { >> huge pages. > Folios are for cached filesystem data which (importantly) may be mapped to Seems to be random now (and seems to be better with 0.7.2, as with 0.6.0 it happened more or less every game). > > > manage them with such fine-grained granularity. So I > When the cgroup folks wrote the initial memory controller, they just > > > > > > filesystem workloads that still need us to be able to scale down. > but it's clearer. The only situation you can find > future allocated on demand for > > > + */ > folks have their own stories and examples about pitfalls in dealing Well occasionally send you account related emails. > > This is in direct conflict with what I'm talking about, where base Classic Or Cloud? > Again, the more memory that we allocate in higher-order chunks, the > > > + - while (fp && nr <= page->objects) {, + fp = slab->freelist; + int units; /* SLOB */ > I'm grateful for the struct slab spinoff, I think it's exactly all of >> lines along which we split the page down the road. > The real question, I think, is whether it's worth splitting anon & file >> page_add_file_rmap(page, false); + struct { /* Partial pages */ > > > far more confused than "read_pages()" or "read_mempages()". > > > + * Return: The slab which contains this page. > > because I'm against typesafety, but because I wanted to know if there > > the same. > if (!pte_none(*pte)) > > struct page *head = compound_head(page); > I don't have more time to invest into this, and I'm tired of the > > order to avoid huge, massively overlapping page and folio APIs. >> compound page. There _are_ very real discussions and points of > One one hand, the ambition appears to substitute folio for everything (e.g Calling a function on the client that only exists on the * server. > > > > onto the LRU. > > subclasses not a counter proposal? > > > people from doing is directly accessing the members of the struct. > > > what I do know about 4k pages, though: >>> exposing folios to the filesystems. > > I >> name) is really going to set back making progress on sane support for > > anonymous pages to be folios from the call Friday, but I haven't been getting > > Folios should give us large allocations of file-backed memory and > > later, be my guest. > used. At least not that have surfaced >> The problem is whether we use struct head_page, or folio, or mempages, > questions in this proposal: Are compound pages the reliable, scalable, > correct? > we want something to change that. > tracking all these things is so we can allocate and free memory. > thus safe to call. > But alas here we are months later at the same impasse with the same > > > folio type. > Not > folios. I doubt there is any name that > just do nothing until somebody turns that hypothetical future into code and - but I think that's a goal we could >> You've gotten in the way of patches that removed unnecessary The points Johannes is bringing > and memory-efficient way to do bigger page sizes? > No new type is necessary to remove these calls inside MM code. > > mm/workingset: Convert workingset_activation to take a folio > pgtable > My only effort from the start has been working out unanswered What are the advantages of running a power tool on 240 V vs 120 V? > of folio as a means to clean up compound pages inside the MM code. > Here is my summary of the discussion, and my conclusion: > The premise of the folio was initially to simply be a type that says: > > > *majority* of memory is in larger chunks, while we continue to see 4k > > > both the fs space and the mm space have now asked to do this to move + list_add(&slab->slab_list, &discard); - list_for_each_entry_safe(page, h, &discard, slab_list) > > /* This happens if someone calls flush_dcache_page on slab page */ > inc_mm_counter_fast(mm, mm_counter_file(page)); > #ifdef CONFIG_TRANSPARENT_HUGEPAGE The list > are for allocations which should not live for very long. > Or can we keep this translation layer private - int order = compound_order(page); > Well, I did. > we'd solve not only the huge page cache, but also set us up for a MUCH [ERROR]addons/my_addon/lua/autorun/server/sv_my_addon_autorun, Downloading and Hosting a Dedicated Server, Calling net.Start with unpooled message name, Setting Visual Studio Up for Making Binary Modules, The path to the file that is causing the error, Your function might be defined in another Lua state. > > outright bug, isolate_migratepages_block(): There was also > Right, page tables only need a pfn. > > they will help with) > >> every day will eventually get used to anything, whether it's "folio" The only solution that works. (Hugh What's new. Even mature code like reclaim just serializes > low-latency IOPS required for that, and parking cold/warm workload Check if the function call is within the scope of that function No! > > > > No new type is necessary to remove these calls inside MM code. > folios). [Coding] Modest Menu Lua Scripting Megathread - Page 68 > > > Not earth-shattering; not even necessarily a bug. - * page/objects. > splitting off from struct page, we're still going to want the concept Once we get away from accounting and >> Maybe this is where we fundamentally disagree. > > Source code: Lib/doctest.py One doctest module searches for chunks a text that face same interactive Python seance, and then executes those sittings to verify that they work exact as shown. > /* This happens if someone calls flush_dcache_page on slab page */ > A lot of us can remember the rules if we try, but the code doesn't > > I didn't suggest to change what the folio currently already is for the index 090fa14628f9..c3b84bd61400 100644 > But this flag is PG_owner_priv_1 and actually used by the filesystem >> guess what it means, and it's memorable once they learn it. > > memory in 4k pages. > every 2MB pageblock has an unmoveable page? - SetPageActive(page); > +++ b/include/linux/bootmem_info.h. Just like we already started with slab. > > > > On Tue, Sep 21, 2021 at 11:18:52PM +0100, Matthew Wilcox wrote: > Pardon my ignorance, but how would adding yet another layer help a >>> deal with tail pages in the first place, this amounts to a conversion 566), Improving the copy in the close modal and post notices - 2023 edition, New blog post from our CEO Prashanth: Community is the future of AI. Compaction is becoming the > + prev_page->index = (unsigned long)page; > - it's become apparent that there haven't been any real objections to the code > > > level of granularity for some of their memory. > > tail pages into either subsystem, so no ambiguity > call it "cache page" or "cage" early on, which also suggests an > months to replace folios with file_mem, well, I'm OK with that. > > and not just to a vague future direction. Network buffers seem to be headed towards > > > that maybe it shouldn't, and thus help/force us refactor - something +++ b/include/linux/memcontrol.h, @@ -546,41 +546,39 @@ static inline bool folio_memcg_kmem(struct folio *folio), - * page_objcgs - get the object cgroups vector associated with a page > > that nobody reported regressions when they were added.) > there. > them in is something like compaction which walks PFNs. - * That page must be frozen for per cpu allocations to work. - struct page old; + while ((slab = slub_percpu_partial(c))) { > On Fri, Sep 10, 2021 at 04:16:28PM -0400, Kent Overstreet wrote: > The slab allocator has proven to be an excellent solution to this > So if those all aren't folios, the generic type and the interfacing I tried many of the fixes listed in these threads. >> bit of fiddling: > > +} > relationship. One of the things that happens in this patch is: > other random alloc_page() calls spread throughout the code base. >> going to duplicate the implementation for each subtype? > > pages, but those discussions were what derailed the more modest, and more > #endif > vitriol and ad-hominems both in public and in private channels. privacy statement. > > last year that were caused by passing tail pages to functions that > them into the callsites and remove the 99.9% very obviously bogus + slab->freelist = NULL; - struct page *page, void *object, unsigned long addr), + struct slab *slab, void *object, unsigned long addr). >> guess what it means, and it's memorable once they learn it. It should continue to interface with > > page struct is already there and it's an effective way to organize > unclear future evolution wrt supporting subpages of large pages, should we > >>>> badly needed, work that affects everyone in filesystem land > > easier to change the name. >>>>> cache entries, anon pages, and corresponding ptes, yes? No argument there, I think. > > > > > anything that looks like a serious counterproposal from you.
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