store_swapout.cc

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/*
 * Copyright (C) 1996-2025 The Squid Software Foundation and contributors
 *
 * Squid software is distributed under GPLv2+ license and includes
 * contributions from numerous individuals and organizations.
 * Please see the COPYING and CONTRIBUTORS files for details.
 */
 
/* DEBUG: section 20    Storage Manager Swapout Functions */
 
#include "squid.h"
#include "base/IoManip.h"
#include "cbdata.h"
#include "CollapsedForwarding.h"
#include "globals.h"
#include "Store.h"
#include "StoreClient.h"
// TODO: Abstract the use of this more
#include "mem_node.h"
#include "MemObject.h"
#include "SquidConfig.h"
#include "StatCounters.h"
#include "store/Disk.h"
#include "store/Disks.h"
#include "store_log.h"
#include "swap_log_op.h"
 
static void storeSwapOutStart(StoreEntry * e);
static StoreIOState::STIOCB storeSwapOutFileClosed;
 
// wrapper to cross C/C++ ABI boundary. xfree is extern "C" for libraries.
static void xfree_cppwrapper(void *x)
{
    xfree(x);
}
 
/* start swapping object to disk */
static void
storeSwapOutStart(StoreEntry * e)
{
    MemObject *mem = e->mem_obj;
    StoreIOState::Pointer sio;
    assert(mem);
    /* Build the swap metadata, so the filesystem will know how much
     * metadata there is to store
     */
    debugs(20, 5, "storeSwapOutStart: Begin SwapOut '" << e->url() << "' to dirno " <<
           e->swap_dirn << ", fileno " << asHex(e->swap_filen).upperCase().minDigits(8));
    /* If we start swapping out objects with OutOfBand Metadata,
     * then this code needs changing
     */
 
    /* TODO: make some sort of data,size refcounted immutable buffer
     * and stop fooling ourselves with "const char*" buffers.
     */
 
    // Create metadata now, possibly in vain: storeCreate needs swap_hdr_sz.
    const auto buf = e->getSerialisedMetaData(mem->swap_hdr_sz);
    assert(buf);
 
    /* Create the swap file */
    generic_cbdata *c = new generic_cbdata(e);
    sio = storeCreate(e, storeSwapOutFileClosed, c);
 
    if (sio == nullptr) {
        assert(!e->hasDisk());
        e->swap_status = SWAPOUT_NONE;
        e->swapOutDecision(MemObject::SwapOut::swImpossible);
        delete c;
        xfree((char*)buf);
        storeLog(STORE_LOG_SWAPOUTFAIL, e);
        return;
    }
 
    mem->swapout.sio = sio;
    /* Don't lock until after create, or the replacement
     * code might get confused */
 
    e->lock("storeSwapOutStart");
    /* Pick up the file number if it was assigned immediately */
    e->attachToDisk(mem->swapout.sio->swap_dirn, mem->swapout.sio->swap_filen, SWAPOUT_WRITING);
 
    e->swapOutDecision(MemObject::SwapOut::swStarted); // after SWAPOUT_WRITING
 
    /* write out the swap metadata */
    storeIOWrite(mem->swapout.sio, buf, mem->swap_hdr_sz, 0, xfree_cppwrapper);
}
 
static bool
doPages(StoreEntry *anEntry)
{
    MemObject *mem = anEntry->mem_obj;
 
    do {
        // find the page containing the first byte we have not swapped out yet
        mem_node *page =
            mem->data_hdr.getBlockContainingLocation(mem->swapout.queue_offset);
 
        if (!page)
            break; // wait for more data to become available
 
        // memNodeWriteComplete() and absence of buffer offset math below
        // imply that we always write from the very beginning of the page
        assert(page->start() == mem->swapout.queue_offset);
 
        /*
         * Get the length of this buffer. We are assuming(!) that the buffer
         * length won't change on this buffer, or things are going to be very
         * strange. I think that after the copy to a buffer is done, the buffer
         * size should stay fixed regardless so that this code isn't confused,
         * but we can look at this at a later date or whenever the code results
         * in bad swapouts, whichever happens first. :-)
         */
        ssize_t swap_buf_len = page->nodeBuffer.length;
 
        debugs(20, 3, "storeSwapOut: swap_buf_len = " << swap_buf_len);
 
        assert(swap_buf_len > 0);
 
        debugs(20, 3, "storeSwapOut: swapping out " << swap_buf_len << " bytes from " << mem->swapout.queue_offset);
 
        mem->swapout.queue_offset += swap_buf_len;
 
        // Quit if write() fails. Sio is going to call our callback, and that
        // will cleanup, but, depending on the fs, that call may be async.
        const bool ok = mem->swapout.sio->write(
                            mem->data_hdr.NodeGet(page),
                            swap_buf_len,
                            -1,
                            memNodeWriteComplete);
 
        if (!ok || !anEntry->swappingOut())
            return false;
 
        int64_t swapout_size = mem->endOffset() - mem->swapout.queue_offset;
 
        if (anEntry->store_status == STORE_PENDING)
            if (swapout_size < SM_PAGE_SIZE)
                break;
 
        if (swapout_size <= 0)
            break;
    } while (true);
 
    // either wait for more data or call swapOutFileClose()
    return true;
}
 
/* This routine is called every time data is sent to the client side.
 * It's overhead is therefor, significant.
 */
void
StoreEntry::swapOut()
{
    if (!mem_obj)
        return;
 
    // this flag may change so we must check even if we are swappingOut
    if (EBIT_TEST(flags, ENTRY_ABORTED)) {
        assert(EBIT_TEST(flags, RELEASE_REQUEST));
        // StoreEntry::abort() already closed the swap out file, if any
        // no trimming: data producer must stop production if ENTRY_ABORTED
        return;
    }
 
    const bool weAreOrMayBeSwappingOut = swappingOut() || mayStartSwapOut();
 
    Store::Root().memoryOut(*this, weAreOrMayBeSwappingOut);
 
    if (mem_obj->swapout.decision < MemObject::SwapOut::swPossible)
        return; // decided not to write to disk (at least for now)
 
    if (!weAreOrMayBeSwappingOut)
        return; // finished writing to disk after an earlier swStarted decision
 
    // Aborted entries have STORE_OK, but swapoutPossible rejects them. Thus,
    // store_status == STORE_OK below means we got everything we wanted.
 
    debugs(20, 7, "storeSwapOut: mem->inmem_lo = " << mem_obj->inmem_lo);
    debugs(20, 7, "storeSwapOut: mem->endOffset() = " << mem_obj->endOffset());
    debugs(20, 7, "storeSwapOut: swapout.queue_offset = " << mem_obj->swapout.queue_offset);
 
    if (mem_obj->swapout.sio != nullptr)
        debugs(20, 7, "storeSwapOut: storeOffset() = " << mem_obj->swapout.sio->offset()  );
 
    int64_t const lowest_offset = mem_obj->lowestMemReaderOffset();
 
    debugs(20, 7, "storeSwapOut: lowest_offset = " << lowest_offset);
 
#if SIZEOF_OFF_T <= 4
 
    if (mem_obj->endOffset() > 0x7FFF0000) {
        debugs(20, DBG_CRITICAL, "WARNING: preventing off_t overflow for " << url());
        abort();
        return;
    }
 
#endif
    if (swappingOut())
        assert(mem_obj->inmem_lo <=  mem_obj->objectBytesOnDisk() );
 
    // buffered bytes we have not swapped out yet
    const int64_t swapout_maxsize = mem_obj->availableForSwapOut();
    assert(swapout_maxsize >= 0);
    debugs(20, 7, "storeSwapOut: swapout_size = " << swapout_maxsize);
 
    if (swapout_maxsize == 0) { // swapped everything we got
        if (store_status == STORE_OK) { // got everything we wanted
            assert(mem_obj->object_sz >= 0);
            swapOutFileClose(StoreIOState::wroteAll);
        }
        // else need more data to swap out
        return;
    }
 
    if (store_status == STORE_PENDING) {
        /* wait for a full block to write */
 
        if (swapout_maxsize < SM_PAGE_SIZE)
            return;
 
        /*
         * Wait until we are below the disk FD limit, only if the
         * next read won't be deferred.
         */
        if (storeTooManyDiskFilesOpen() && !checkDeferRead(-1))
            return;
    }
 
    /* Ok, we have stuff to swap out.  Is there a swapout.sio open? */
    if (!hasDisk()) {
        assert(mem_obj->swapout.sio == nullptr);
        assert(mem_obj->inmem_lo == 0);
        storeSwapOutStart(this); // sets SwapOut::swImpossible on failures
    }
 
    if (mem_obj->swapout.sio == nullptr)
        return;
 
    if (!doPages(this))
        /* oops, we're not swapping out any more */
        return;
 
    if (store_status == STORE_OK) {
        /*
         * If the state is STORE_OK, then all data must have been given
         * to the filesystem at this point because storeSwapOut() is
         * not going to be called again for this entry.
         */
        assert(mem_obj->object_sz >= 0);
        assert(mem_obj->endOffset() == mem_obj->swapout.queue_offset);
        swapOutFileClose(StoreIOState::wroteAll);
    }
}
 
void
StoreEntry::swapOutFileClose(int how)
{
    assert(mem_obj != nullptr);
    debugs(20, 3, "storeSwapOutFileClose: " << getMD5Text() << " how=" << how);
    debugs(20, 3, "storeSwapOutFileClose: sio = " << mem_obj->swapout.sio.getRaw());
 
    if (mem_obj->swapout.sio == nullptr)
        return;
 
    storeClose(mem_obj->swapout.sio, how);
}
 
static void
storeSwapOutFileClosed(void *data, int errflag, StoreIOState::Pointer self)
{
    StoreEntry *e;
    static_cast<generic_cbdata *>(data)->unwrap(&e);
 
    MemObject *mem = e->mem_obj;
    assert(mem->swapout.sio == self);
    assert(e->swappingOut());
 
    // if object_size is still unknown, the entry was probably aborted
    if (errflag || e->objectLen() < 0) {
        debugs(20, 2, "storeSwapOutFileClosed: dirno " << e->swap_dirn << ", swapfile " <<
               asHex(e->swap_filen).upperCase().minDigits(8) <<
               ", errflag=" << errflag);
 
        if (errflag == DISK_NO_SPACE_LEFT) {
            /* TODO: this should be handle by the link from store IO to
             * Store, rather than being a top level API call.
             */
            e->disk().diskFull();
            storeConfigure();
        }
 
        // mark the locked entry for deletion
        // TODO: Keep the memory entry (if any)
        e->releaseRequest();
        e->swap_status = SWAPOUT_FAILED;
        e->disk().finalizeSwapoutFailure(*e);
    } else {
        /* swapping complete */
        debugs(20, 3, "storeSwapOutFileClosed: SwapOut complete: '" << e->url() << "' to " <<
               e->swap_dirn  << ", " << asHex(e->swap_filen).upperCase().minDigits(8));
        debugs(20, 5, "swap_file_sz = " <<
               e->objectLen() << " + " << mem->swap_hdr_sz);
 
        e->swap_file_sz = e->objectLen() + mem->swap_hdr_sz;
        e->swap_status = SWAPOUT_DONE;
        e->disk().finalizeSwapoutSuccess(*e);
 
        // XXX: For some Stores, it is pointless to re-check cachability here
        // and it leads to double counts in store_check_cachable_hist. We need
        // another way to signal a completed but failed swapout. Or, better,
        // each Store should handle its own logging and LOG state setting.
        if (e->checkCachable()) {
            storeLog(STORE_LOG_SWAPOUT, e);
            storeDirSwapLog(e, SWAP_LOG_ADD);
        }
 
        ++statCounter.swap.outs;
    }
 
    debugs(20, 3, "storeSwapOutFileClosed: " << __FILE__ << ":" << __LINE__);
    mem->swapout.sio = nullptr;
    e->storeWriterDone(); // after updating swap_status
    e->unlock("storeSwapOutFileClosed");
}
 
bool
StoreEntry::mayStartSwapOut()
{
    // must be checked in the caller
    assert(!EBIT_TEST(flags, ENTRY_ABORTED));
    assert(!swappingOut());
 
    if (!Config.cacheSwap.n_configured)
        return false;
 
    assert(mem_obj);
    const MemObject::SwapOut::Decision &decision = mem_obj->swapout.decision;
 
    // if we decided that starting is not possible, do not repeat same checks
    if (decision == MemObject::SwapOut::swImpossible) {
        debugs(20, 3, " already rejected");
        return false;
    }
 
    // If we have started swapping out, do not start over. Most likely, we have
    // finished swapping out by now because we are not currently swappingOut().
    if (decision == MemObject::SwapOut::swStarted) {
        debugs(20, 3, "already started");
        return false;
    }
 
    if (shutting_down) {
        debugs(20, 3, "avoid heavy optional work during shutdown");
        swapOutDecision(MemObject::SwapOut::swImpossible);
        return false;
    }
 
    // if there is a usable disk entry already, do not start over
    if (hasDisk() || Store::Root().hasReadableDiskEntry(*this)) {
        debugs(20, 3, "already did"); // we or somebody else created that entry
        swapOutDecision(MemObject::SwapOut::swImpossible);
        return false;
    }
 
    if (Store::Root().markedForDeletionAndAbandoned(*this)) {
        debugs(20, 3, "marked for deletion and abandoned");
        swapOutDecision(MemObject::SwapOut::swImpossible);
        return false;
    }
 
    // if we decided that swapout is possible, do not repeat same checks
    if (decision == MemObject::SwapOut::swPossible) {
        debugs(20, 3, "already allowed");
        return true;
    }
 
    // To avoid SMP workers releasing each other caching attempts, restrict disk
    // caching to StoreEntry publisher. This check goes before checkCachable()
    // that may incorrectly release() publisher's entry.
    if (Store::Root().transientsReader(*this)) {
        debugs(20, 5, "yield to entry publisher");
        swapOutDecision(MemObject::SwapOut::swImpossible);
        return false;
    }
 
    if (!checkCachable()) {
        debugs(20, 3, "not cachable");
        swapOutDecision(MemObject::SwapOut::swImpossible);
        return false;
    }
 
    if (EBIT_TEST(flags, ENTRY_SPECIAL)) {
        debugs(20, 3, url() << " SPECIAL");
        swapOutDecision(MemObject::SwapOut::swImpossible);
        return false;
    }
 
    if (mem_obj->inmem_lo > 0) {
        debugs(20, 3, "storeSwapOut: (inmem_lo > 0)  imem_lo:" <<  mem_obj->inmem_lo);
        swapOutDecision(MemObject::SwapOut::swImpossible);
        return false;
    }
 
    if (!mem_obj->isContiguous()) {
        debugs(20, 3, "storeSwapOut: not Contiguous");
        swapOutDecision(MemObject::SwapOut::swImpossible);
        return false;
    }
 
    // handle store_maxobjsize limit
    {
        // TODO: add estimated store metadata size to be conservative
 
        // use guaranteed maximum if it is known
        const int64_t expectedEnd = mem_obj->expectedReplySize();
        debugs(20, 7, "expectedEnd = " << expectedEnd);
        if (expectedEnd > store_maxobjsize) {
            debugs(20, 3, "will not fit: " << expectedEnd <<
                   " > " << store_maxobjsize);
            swapOutDecision(MemObject::SwapOut::swImpossible);
            return false; // known to outgrow the limit eventually
        }
 
        // use current minimum (always known)
        const int64_t currentEnd = mem_obj->endOffset();
        if (currentEnd > store_maxobjsize) {
            debugs(20, 3, "does not fit: " << currentEnd <<
                   " > " << store_maxobjsize);
            swapOutDecision(MemObject::SwapOut::swImpossible);
            return false; // already does not fit and may only get bigger
        }
 
        // prevent final default swPossible answer for yet unknown length
        if (expectedEnd < 0 && store_status != STORE_OK) {
            const int64_t more = Store::Root().accumulateMore(*this);
            if (more > 0) {
                debugs(20, 5, "got " << currentEnd << "; defer decision for " << more << " more bytes");
                return true; // may still fit, but no final decision yet
            }
        }
    }
 
    swapOutDecision(MemObject::SwapOut::swPossible);
    return true;
}