On 05/07/2024 09:59, David Hildenbrand wrote: > On 05.07.24 10:45, Ryan Roberts wrote: >> On 05/07/2024 06:47, Baolin Wang wrote: >>> >>> >>> On 2024/7/5 03:49, Matthew Wilcox wrote: >>>> On Thu, Jul 04, 2024 at 09:19:10PM +0200, David Hildenbrand wrote: >>>>> On 04.07.24 21:03, David Hildenbrand wrote: >>>>>>> shmem has two uses: >>>>>>> >>>>>>> - MAP_ANONYMOUS | MAP_SHARED (this patch set) >>>>>>> - tmpfs >>>>>>> >>>>>>> For the second use case we don't want controls *at all*, we want the >>>>>>> same heiristics used for all other filesystems to apply to tmpfs. >>>>>> >>>>>> As discussed in the MM meeting, Hugh had a different opinion on that. >>>>> >>>>> FWIW, I just recalled that I wrote a quick summary: >>>>> >>>>> https://lkml.kernel.org/r/f1783ff0-65bd-4b2b-8952-52b6822a0835@xxxxxxxxxx >>>>> >>>>> I believe the meetings are recorded as well, but never looked at recordings. >>>> >>>> That's not what I understood Hugh to mean. To me, it seemed that Hugh >>>> was expressing an opinion on using shmem as shmem, not as using it as >>>> tmpfs. >>>> >>>> If I misunderstood Hugh, well, I still disagree. We should not have >>>> separate controls for this. tmpfs is just not that special. >> >> I wasn't at the meeting that's being referred to, but I thought we previously >> agreed that tmpfs *is* special because in some configurations its not backed by >> swap so is locked in ram? > > There are multiple things to that, like: > > * Machines only having limited/no swap configured > * tmpfs can be configured to never go to swap > * memfd/tmpfs files getting used purely for mmap(): there is no real > difference to MAP_ANON|MAP_SHARE besides the processes we share that > memory with. > > Especially when it comes to memory waste concerns and access behavior in some > cases, tmpfs behaved much more like anonymous memory. But there are for sure > other use cases where tmpfs is not that special. > > My opinion is that we need to let people configure orders (if you feel like it, > configure all), but *select* the order to allocate based on readahead > information -- in contrast to anonymous memory where we start at the highest > order and don't have readahead information available. That approach is exactly what I proposed to start playing with yesterday [1] for regular pagecache folio allocations too :) [1] https://lore.kernel.org/linux-mm/bdde4008-60db-4717-a6b5-53d77ab76bdb@xxxxxxx/ > > Maybe we need different "order allcoation" logic for read/write vs. fault, not > sure. > > But I don't maintain that code, so I can only give stupid suggestions and repeat > what I understood from the meeting with Hugh and Kirill :) >
